Source/WebCore/rendering/RenderBlockFlow.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003-2013 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */

 #include "config.h"
 #include "RenderBlockFlow.h"

 #include "Editor.h"
 #include "FloatingObjects.h"
 #include "Frame.h"
 #include "HitTestLocation.h"
 #include "InlineTextBox.h"
 #include "LayoutRepainter.h"
 #include "RenderFlowThread.h"
 #include "RenderLayer.h"
 #include "RenderNamedFlowFragment.h"
 #include "RenderText.h"
 #include "RenderView.h"
 #include "SimpleLineLayoutFunctions.h"
 #include "VerticalPositionCache.h"
 #include "VisiblePosition.h"

 using namespace std;

 namespace WebCore {

 bool RenderBlock::s_canPropagateFloatIntoSibling = false;

 struct SameSizeAsMarginInfo {
     uint32_t bitfields : 16;
     LayoutUnit margins[2];
 };

 COMPILE_ASSERT(sizeof(RenderBlockFlow::MarginValues) == sizeof(LayoutUnit[4]), MarginValues_should_stay_small);
 COMPILE_ASSERT(sizeof(RenderBlockFlow::MarginInfo) == sizeof(SameSizeAsMarginInfo), MarginInfo_should_stay_small);

 // Our MarginInfo state used when laying out block children.
 RenderBlockFlow::MarginInfo::MarginInfo(RenderBlockFlow& block, LayoutUnit beforeBorderPadding, LayoutUnit afterBorderPadding)
     : m_atBeforeSideOfBlock(true)
     , m_atAfterSideOfBlock(false)
     , m_hasMarginBeforeQuirk(false)
     , m_hasMarginAfterQuirk(false)
     , m_determinedMarginBeforeQuirk(false)
     , m_discardMargin(false)
 {
     const RenderStyle& blockStyle = block.style();
     ASSERT(block.isRenderView() || block.parent());
     m_canCollapseWithChildren = !block.isRenderView() && !block.isRoot() && !block.isOutOfFlowPositioned()
         && !block.isFloating() && !block.isTableCell() && !block.hasOverflowClip() && !block.isInlineBlockOrInlineTable()
         && !block.isRenderFlowThread() && !block.isWritingModeRoot() && !block.parent()->isFlexibleBox()
         && blockStyle.hasAutoColumnCount() && blockStyle.hasAutoColumnWidth() && !blockStyle.columnSpan();

     m_canCollapseMarginBeforeWithChildren = m_canCollapseWithChildren && !beforeBorderPadding && blockStyle.marginBeforeCollapse() != MSEPARATE;

     // If any height other than auto is specified in CSS, then we don't collapse our bottom
     // margins with our children's margins. To do otherwise would be to risk odd visual
     // effects when the children overflow out of the parent block and yet still collapse
     // with it. We also don't collapse if we have any bottom border/padding.
     m_canCollapseMarginAfterWithChildren = m_canCollapseWithChildren && !afterBorderPadding
         && (blockStyle.logicalHeight().isAuto() && !blockStyle.logicalHeight().value()) && blockStyle.marginAfterCollapse() != MSEPARATE;

     m_quirkContainer = block.isTableCell() || block.isBody();

     m_discardMargin = m_canCollapseMarginBeforeWithChildren && block.mustDiscardMarginBefore();

     m_positiveMargin = (m_canCollapseMarginBeforeWithChildren && !block.mustDiscardMarginBefore()) ? block.maxPositiveMarginBefore() : LayoutUnit();
     m_negativeMargin = (m_canCollapseMarginBeforeWithChildren && !block.mustDiscardMarginBefore()) ? block.maxNegativeMarginBefore() : LayoutUnit();
 }

 RenderBlockFlow::RenderBlockFlow(Element& element, PassRef<RenderStyle> style)
     : RenderBlock(element, std::move(style), RenderBlockFlowFlag)
 {
     setChildrenInline(true);
 }

 RenderBlockFlow::RenderBlockFlow(Document& document, PassRef<RenderStyle> style)
     : RenderBlock(document, std::move(style), RenderBlockFlowFlag)
 {
     setChildrenInline(true);
 }

 RenderBlockFlow::~RenderBlockFlow()
 {
 }

 void RenderBlockFlow::insertedIntoTree()
 {
     RenderBlock::insertedIntoTree();
     createRenderNamedFlowFragmentIfNeeded();
 }

 void RenderBlockFlow::willBeDestroyed()
 {
     // Mark as being destroyed to avoid trouble with merges in removeChild().
     m_beingDestroyed = true;

     delete lineGridBox();

     if (renderNamedFlowFragment())
         setRenderNamedFlowFragment(0);

     if (!documentBeingDestroyed()) {
         if (firstChild() && firstChild()->isRunIn())
             moveRunInToOriginalPosition(*firstChild());
     }

     // Make sure to destroy anonymous children first while they are still connected to the rest of the tree, so that they will
     // properly dirty line boxes that they are removed from. Effects that do :before/:after only on hover could crash otherwise.
     destroyLeftoverChildren();

     // Destroy our continuation before anything other than anonymous children.
     // The reason we don't destroy it before anonymous children is that they may
     // have continuations of their own that are anonymous children of our continuation.
     RenderBoxModelObject* continuation = this->continuation();
     if (continuation) {
         continuation->destroy();
         setContinuation(0);
     }

     if (!documentBeingDestroyed()) {
         if (firstLineBox()) {
             // We can't wait for RenderBox::destroy to clear the selection,
             // because by then we will have nuked the line boxes.
             // FIXME: The FrameSelection should be responsible for this when it
             // is notified of DOM mutations.
             if (isSelectionBorder())
                 view().clearSelection();

             // If we are an anonymous block, then our line boxes might have children
             // that will outlast this block. In the non-anonymous block case those
             // children will be destroyed by the time we return from this function.
             if (isAnonymousBlock()) {
                 for (auto box = firstLineBox(); box; box = box->nextLineBox()) {
                     while (auto childBox = box->firstChild())
                         childBox->removeFromParent();
                 }
             }
         } else if (parent())
             parent()->dirtyLinesFromChangedChild(this);
     }

     m_lineBoxes.deleteLineBoxes();

     removeFromDelayedUpdateScrollInfoSet();

     // NOTE: This jumps down to RenderBox, bypassing RenderBlock since it would do duplicate work.
     RenderBox::willBeDestroyed();
 }

 void RenderBlockFlow::clearFloats()
 {
     if (m_floatingObjects)
         m_floatingObjects->setHorizontalWritingMode(isHorizontalWritingMode());

     HashSet<RenderBox*> oldIntrudingFloatSet;
     if (!childrenInline() && m_floatingObjects) {
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         auto end = floatingObjectSet.end();
         for (auto it = floatingObjectSet.begin(); it != end; ++it) {
             FloatingObject* floatingObject = it->get();
             if (!floatingObject->isDescendant())
                 oldIntrudingFloatSet.add(&floatingObject->renderer());
         }
     }

     // Inline blocks are covered by the isReplaced() check in the avoidFloats method.
     if (avoidsFloats() || isRoot() || isRenderView() || isFloatingOrOutOfFlowPositioned() || isTableCell()) {
         if (m_floatingObjects)
             m_floatingObjects->clear();
         if (!oldIntrudingFloatSet.isEmpty())
             markAllDescendantsWithFloatsForLayout();
         return;
     }

     RendererToFloatInfoMap floatMap;

     if (m_floatingObjects) {
         if (childrenInline())
             m_floatingObjects->moveAllToFloatInfoMap(floatMap);
         else
             m_floatingObjects->clear();
     }

     // We should not process floats if the parent node is not a RenderBlock. Otherwise, we will add
     // floats in an invalid context. This will cause a crash arising from a bad cast on the parent.
     // See <rdar://problem/8049753>, where float property is applied on a text node in a SVG.
     if (!parent() || !parent()->isRenderBlockFlow())
         return;

     // Attempt to locate a previous sibling with overhanging floats. We skip any elements that are
     // out of flow (like floating/positioned elements), and we also skip over any objects that may have shifted
     // to avoid floats.
     RenderBlockFlow* parentBlock = toRenderBlockFlow(parent());
     bool parentHasFloats = false;
     RenderObject* prev = previousSibling();
     while (prev && (prev->isFloatingOrOutOfFlowPositioned() || !prev->isBox() || !prev->isRenderBlockFlow() || toRenderBlockFlow(prev)->avoidsFloats())) {
         if (prev->isFloating())
             parentHasFloats = true;
         prev = prev->previousSibling();
     }

     // First add in floats from the parent.
     LayoutUnit logicalTopOffset = logicalTop();
     if (parentHasFloats)
         addIntrudingFloats(parentBlock, parentBlock->logicalLeftOffsetForContent(), logicalTopOffset);

     LayoutUnit logicalLeftOffset = 0;
     if (prev)
         logicalTopOffset -= toRenderBox(prev)->logicalTop();
     else {
         prev = parentBlock;
         logicalLeftOffset += parentBlock->logicalLeftOffsetForContent();
     }

     // Add overhanging floats from the previous RenderBlock, but only if it has a float that intrudes into our space.
     RenderBlockFlow* block = toRenderBlockFlow(prev);
     if (block->m_floatingObjects && block->lowestFloatLogicalBottom() > logicalTopOffset)
         addIntrudingFloats(block, logicalLeftOffset, logicalTopOffset);

     if (childrenInline()) {
         LayoutUnit changeLogicalTop = LayoutUnit::max();
         LayoutUnit changeLogicalBottom = LayoutUnit::min();
         if (m_floatingObjects) {
             const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
             auto end = floatingObjectSet.end();
             for (auto it = floatingObjectSet.begin(); it != end; ++it) {
                 FloatingObject* floatingObject = it->get();
                 std::unique_ptr<FloatingObject> oldFloatingObject = floatMap.take(&floatingObject->renderer());
                 LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);
                 if (oldFloatingObject) {
                     LayoutUnit oldLogicalBottom = logicalBottomForFloat(oldFloatingObject.get());
                     if (logicalWidthForFloat(floatingObject) != logicalWidthForFloat(oldFloatingObject.get()) || logicalLeftForFloat(floatingObject) != logicalLeftForFloat(oldFloatingObject.get())) {
                         changeLogicalTop = 0;
                         changeLogicalBottom = max(changeLogicalBottom, max(logicalBottom, oldLogicalBottom));
                     } else {
                         if (logicalBottom != oldLogicalBottom) {
                             changeLogicalTop = min(changeLogicalTop, min(logicalBottom, oldLogicalBottom));
                             changeLogicalBottom = max(changeLogicalBottom, max(logicalBottom, oldLogicalBottom));
                         }
                         LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
                         LayoutUnit oldLogicalTop = logicalTopForFloat(oldFloatingObject.get());
                         if (logicalTop != oldLogicalTop) {
                             changeLogicalTop = min(changeLogicalTop, min(logicalTop, oldLogicalTop));
                             changeLogicalBottom = max(changeLogicalBottom, max(logicalTop, oldLogicalTop));
                         }
                     }

                     if (oldFloatingObject->originatingLine() && !selfNeedsLayout()) {
                         ASSERT(&oldFloatingObject->originatingLine()->renderer() == this);
                         oldFloatingObject->originatingLine()->markDirty();
                     }
                 } else {
                     changeLogicalTop = 0;
                     changeLogicalBottom = max(changeLogicalBottom, logicalBottom);
                 }
             }
         }

         auto end = floatMap.end();
         for (auto it = floatMap.begin(); it != end; ++it) {
             FloatingObject* floatingObject = it->value.get();
             if (!floatingObject->isDescendant()) {
                 changeLogicalTop = 0;
                 changeLogicalBottom = max(changeLogicalBottom, logicalBottomForFloat(floatingObject));
             }
         }

         markLinesDirtyInBlockRange(changeLogicalTop, changeLogicalBottom);
     } else if (!oldIntrudingFloatSet.isEmpty()) {
         // If there are previously intruding floats that no longer intrude, then children with floats
         // should also get layout because they might need their floating object lists cleared.
         if (m_floatingObjects->set().size() < oldIntrudingFloatSet.size())
             markAllDescendantsWithFloatsForLayout();
         else {
             const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
             auto end = floatingObjectSet.end();
             for (auto it = floatingObjectSet.begin(); it != end && !oldIntrudingFloatSet.isEmpty(); ++it)
                 oldIntrudingFloatSet.remove(&(*it)->renderer());
             if (!oldIntrudingFloatSet.isEmpty())
                 markAllDescendantsWithFloatsForLayout();
         }
     }
 }

 void RenderBlockFlow::layoutBlock(bool relayoutChildren, LayoutUnit pageLogicalHeight)
 {
     ASSERT(needsLayout());

     if (!relayoutChildren && simplifiedLayout())
         return;

     LayoutRepainter repainter(*this, checkForRepaintDuringLayout());

     if (updateLogicalWidthAndColumnWidth())
         relayoutChildren = true;

     clearFloats();

     LayoutUnit previousHeight = logicalHeight();
     // FIXME: should this start out as borderAndPaddingLogicalHeight() + scrollbarLogicalHeight(),
     // for consistency with other render classes?
     setLogicalHeight(0);

     bool pageLogicalHeightChanged = false;
     bool hasSpecifiedPageLogicalHeight = false;
     checkForPaginationLogicalHeightChange(pageLogicalHeight, pageLogicalHeightChanged, hasSpecifiedPageLogicalHeight);

     const RenderStyle& styleToUse = style();
     LayoutStateMaintainer statePusher(&view(), this, locationOffset(), hasColumns() || hasTransform() || hasReflection() || styleToUse.isFlippedBlocksWritingMode(), pageLogicalHeight, pageLogicalHeightChanged, columnInfo());

     prepareShapesAndPaginationBeforeBlockLayout(relayoutChildren);
     if (!relayoutChildren)
         relayoutChildren = namedFlowFragmentNeedsUpdate();

     // We use four values, maxTopPos, maxTopNeg, maxBottomPos, and maxBottomNeg, to track
     // our current maximal positive and negative margins. These values are used when we
     // are collapsed with adjacent blocks, so for example, if you have block A and B
     // collapsing together, then you'd take the maximal positive margin from both A and B
     // and subtract it from the maximal negative margin from both A and B to get the
     // true collapsed margin. This algorithm is recursive, so when we finish layout()
     // our block knows its current maximal positive/negative values.
     //
     // Start out by setting our margin values to our current margins. Table cells have
     // no margins, so we don't fill in the values for table cells.
     bool isCell = isTableCell();
     if (!isCell) {
         initMaxMarginValues();

         setHasMarginBeforeQuirk(styleToUse.hasMarginBeforeQuirk());
         setHasMarginAfterQuirk(styleToUse.hasMarginAfterQuirk());
         setPaginationStrut(0);
     }

     LayoutUnit repaintLogicalTop = 0;
     LayoutUnit repaintLogicalBottom = 0;
     LayoutUnit maxFloatLogicalBottom = 0;
     if (!firstChild() && !isAnonymousBlock())
         setChildrenInline(true);
     if (childrenInline())
         layoutInlineChildren(relayoutChildren, repaintLogicalTop, repaintLogicalBottom);
     else
         layoutBlockChildren(relayoutChildren, maxFloatLogicalBottom);

     // Expand our intrinsic height to encompass floats.
     LayoutUnit toAdd = borderAndPaddingAfter() + scrollbarLogicalHeight();
     if (lowestFloatLogicalBottom() > (logicalHeight() - toAdd) && expandsToEncloseOverhangingFloats())
         setLogicalHeight(lowestFloatLogicalBottom() + toAdd);

     if (relayoutForPagination(hasSpecifiedPageLogicalHeight, pageLogicalHeight, statePusher) || relayoutToAvoidWidows(statePusher)) {
         ASSERT(!shouldBreakAtLineToAvoidWidow());
         return;
     }

     // Calculate our new height.
     LayoutUnit oldHeight = logicalHeight();
     LayoutUnit oldClientAfterEdge = clientLogicalBottom();

     // Before updating the final size of the flow thread make sure a forced break is applied after the content.
     // This ensures the size information is correctly computed for the last auto-height region receiving content.
     if (isRenderFlowThread())
         toRenderFlowThread(this)->applyBreakAfterContent(oldClientAfterEdge);

     updateLogicalHeight();
     LayoutUnit newHeight = logicalHeight();
     if (oldHeight != newHeight) {
         if (oldHeight > newHeight && maxFloatLogicalBottom > newHeight && !childrenInline()) {
             // One of our children's floats may have become an overhanging float for us. We need to look for it.
             for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
                 if (child->isRenderBlockFlow() && !child->isFloatingOrOutOfFlowPositioned()) {
                     RenderBlockFlow& block = toRenderBlockFlow(*child);
                     if (block.lowestFloatLogicalBottom() + block.logicalTop() > newHeight)
                         addOverhangingFloats(block, false);
                 }
             }
         }
     }

     bool heightChanged = (previousHeight != newHeight);
     if (heightChanged)
         relayoutChildren = true;

     layoutPositionedObjects(relayoutChildren || isRoot());

     updateShapesAfterBlockLayout(heightChanged);

     // Add overflow from children (unless we're multi-column, since in that case all our child overflow is clipped anyway).
     computeOverflow(oldClientAfterEdge);

     statePusher.pop();

     fitBorderToLinesIfNeeded();

     if (view().layoutState()->m_pageLogicalHeight)
         setPageLogicalOffset(view().layoutState()->pageLogicalOffset(this, logicalTop()));

     updateLayerTransform();

     // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
     // we overflow or not.
     updateScrollInfoAfterLayout();

     // FIXME: This repaint logic should be moved into a separate helper function!
     // Repaint with our new bounds if they are different from our old bounds.
     bool didFullRepaint = repainter.repaintAfterLayout();
     if (!didFullRepaint && repaintLogicalTop != repaintLogicalBottom && (styleToUse.visibility() == VISIBLE || enclosingLayer()->hasVisibleContent())) {
         // FIXME: We could tighten up the left and right invalidation points if we let layoutInlineChildren fill them in based off the particular lines
         // it had to lay out. We wouldn't need the hasOverflowClip() hack in that case either.
         LayoutUnit repaintLogicalLeft = logicalLeftVisualOverflow();
         LayoutUnit repaintLogicalRight = logicalRightVisualOverflow();
         if (hasOverflowClip()) {
             // If we have clipped overflow, we should use layout overflow as well, since visual overflow from lines didn't propagate to our block's overflow.
             // Note the old code did this as well but even for overflow:visible. The addition of hasOverflowClip() at least tightens up the hack a bit.
             // layoutInlineChildren should be patched to compute the entire repaint rect.
             repaintLogicalLeft = min(repaintLogicalLeft, logicalLeftLayoutOverflow());
             repaintLogicalRight = max(repaintLogicalRight, logicalRightLayoutOverflow());
         }

         LayoutRect repaintRect;
         if (isHorizontalWritingMode())
             repaintRect = LayoutRect(repaintLogicalLeft, repaintLogicalTop, repaintLogicalRight - repaintLogicalLeft, repaintLogicalBottom - repaintLogicalTop);
         else
             repaintRect = LayoutRect(repaintLogicalTop, repaintLogicalLeft, repaintLogicalBottom - repaintLogicalTop, repaintLogicalRight - repaintLogicalLeft);

         // The repaint rect may be split across columns, in which case adjustRectForColumns() will return the union.
         adjustRectForColumns(repaintRect);

         repaintRect.inflate(maximalOutlineSize(PaintPhaseOutline));

         if (hasOverflowClip()) {
             // Adjust repaint rect for scroll offset
             repaintRect.move(-scrolledContentOffset());

             // Don't allow this rect to spill out of our overflow box.
             repaintRect.intersect(LayoutRect(LayoutPoint(), size()));
         }

         // Make sure the rect is still non-empty after intersecting for overflow above
         if (!repaintRect.isEmpty()) {
             repaintRectangle(repaintRect); // We need to do a partial repaint of our content.
             if (hasReflection())
                 repaintRectangle(reflectedRect(repaintRect));
         }
     }

     clearNeedsLayout();
 }

 void RenderBlockFlow::layoutBlockChildren(bool relayoutChildren, LayoutUnit& maxFloatLogicalBottom)
 {
     dirtyForLayoutFromPercentageHeightDescendants();

     LayoutUnit beforeEdge = borderAndPaddingBefore();
     LayoutUnit afterEdge = borderAndPaddingAfter() + scrollbarLogicalHeight();

     setLogicalHeight(beforeEdge);

     // Lay out our hypothetical grid line as though it occurs at the top of the block.
     if (view().layoutState()->lineGrid() == this)
         layoutLineGridBox();

     // The margin struct caches all our current margin collapsing state.
     MarginInfo marginInfo(*this, beforeEdge, afterEdge);

     // Fieldsets need to find their legend and position it inside the border of the object.
     // The legend then gets skipped during normal layout. The same is true for ruby text.
     // It doesn't get included in the normal layout process but is instead skipped.
     RenderObject* childToExclude = layoutSpecialExcludedChild(relayoutChildren);

     LayoutUnit previousFloatLogicalBottom = 0;
     maxFloatLogicalBottom = 0;

     RenderBox* next = firstChildBox();

     while (next) {
         RenderBox& child = *next;
         next = child.nextSiblingBox();

         if (childToExclude == &child)
             continue; // Skip this child, since it will be positioned by the specialized subclass (fieldsets and ruby runs).

         updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, child);

         if (child.isOutOfFlowPositioned()) {
             child.containingBlock()->insertPositionedObject(child);
             adjustPositionedBlock(child, marginInfo);
             continue;
         }
         if (child.isFloating()) {
             insertFloatingObject(child);
             adjustFloatingBlock(marginInfo);
             continue;
         }

         // Lay out the child.
         layoutBlockChild(child, marginInfo, previousFloatLogicalBottom, maxFloatLogicalBottom);
     }

     // Now do the handling of the bottom of the block, adding in our bottom border/padding and
     // determining the correct collapsed bottom margin information.
     handleAfterSideOfBlock(beforeEdge, afterEdge, marginInfo);
 }

 void RenderBlockFlow::layoutInlineChildren(bool relayoutChildren, LayoutUnit& repaintLogicalTop, LayoutUnit& repaintLogicalBottom)
 {
     if (m_lineLayoutPath == UndeterminedPath)
         m_lineLayoutPath = SimpleLineLayout::canUseFor(*this) ? SimpleLinesPath : LineBoxesPath;

     if (m_lineLayoutPath == SimpleLinesPath) {
         deleteLineBoxesBeforeSimpleLineLayout();
         layoutSimpleLines(repaintLogicalTop, repaintLogicalBottom);
         return;
     }

     m_simpleLineLayout = nullptr;
     layoutLineBoxes(relayoutChildren, repaintLogicalTop, repaintLogicalBottom);
 }

 void RenderBlockFlow::layoutBlockChild(RenderBox& child, MarginInfo& marginInfo, LayoutUnit& previousFloatLogicalBottom, LayoutUnit& maxFloatLogicalBottom)
 {
     LayoutUnit oldPosMarginBefore = maxPositiveMarginBefore();
     LayoutUnit oldNegMarginBefore = maxNegativeMarginBefore();

     // The child is a normal flow object. Compute the margins we will use for collapsing now.
     child.computeAndSetBlockDirectionMargins(this);

     // Try to guess our correct logical top position. In most cases this guess will
     // be correct. Only if we're wrong (when we compute the real logical top position)
     // will we have to potentially relayout.
     LayoutUnit estimateWithoutPagination;
     LayoutUnit logicalTopEstimate = estimateLogicalTopPosition(child, marginInfo, estimateWithoutPagination);

     // Cache our old rect so that we can dirty the proper repaint rects if the child moves.
     LayoutRect oldRect = child.frameRect();
     LayoutUnit oldLogicalTop = logicalTopForChild(child);

 #if !ASSERT_DISABLED
     LayoutSize oldLayoutDelta = view().layoutDelta();
 #endif
     // Go ahead and position the child as though it didn't collapse with the top.
     setLogicalTopForChild(child, logicalTopEstimate, ApplyLayoutDelta);
     estimateRegionRangeForBoxChild(child);

     RenderBlockFlow* childBlockFlow = child.isRenderBlockFlow() ? toRenderBlockFlow(&child) : nullptr;
     bool markDescendantsWithFloats = false;
     if (logicalTopEstimate != oldLogicalTop && !child.avoidsFloats() && childBlockFlow && childBlockFlow->containsFloats())
         markDescendantsWithFloats = true;
 #if ENABLE(SUBPIXEL_LAYOUT)
     else if (UNLIKELY(logicalTopEstimate.mightBeSaturated()))
         // logicalTopEstimate, returned by estimateLogicalTopPosition, might be saturated for
         // very large elements. If it does the comparison with oldLogicalTop might yield a
         // false negative as adding and removing margins, borders etc from a saturated number
         // might yield incorrect results. If this is the case always mark for layout.
         markDescendantsWithFloats = true;
 #endif
     else if (!child.avoidsFloats() || child.shrinkToAvoidFloats()) {
         // If an element might be affected by the presence of floats, then always mark it for
         // layout.
         LayoutUnit fb = max(previousFloatLogicalBottom, lowestFloatLogicalBottom());
         if (fb > logicalTopEstimate)
             markDescendantsWithFloats = true;
     }

     if (childBlockFlow) {
         if (markDescendantsWithFloats)
             childBlockFlow->markAllDescendantsWithFloatsForLayout();
         if (!child.isWritingModeRoot())
             previousFloatLogicalBottom = max(previousFloatLogicalBottom, oldLogicalTop + childBlockFlow->lowestFloatLogicalBottom());
     }

     if (!child.needsLayout())
         child.markForPaginationRelayoutIfNeeded();

     bool childHadLayout = child.everHadLayout();
     bool childNeededLayout = child.needsLayout();
     if (childNeededLayout)
         child.layout();

     // Cache if we are at the top of the block right now.
     bool atBeforeSideOfBlock = marginInfo.atBeforeSideOfBlock();

     // Now determine the correct ypos based off examination of collapsing margin
     // values.
     LayoutUnit logicalTopBeforeClear = collapseMargins(child, marginInfo);

     // Now check for clear.
     LayoutUnit logicalTopAfterClear = clearFloatsIfNeeded(child, marginInfo, oldPosMarginBefore, oldNegMarginBefore, logicalTopBeforeClear);

     bool paginated = view().layoutState()->isPaginated();
     if (paginated)
         logicalTopAfterClear = adjustBlockChildForPagination(logicalTopAfterClear, estimateWithoutPagination, child, atBeforeSideOfBlock && logicalTopBeforeClear == logicalTopAfterClear);

     setLogicalTopForChild(child, logicalTopAfterClear, ApplyLayoutDelta);

     // Now we have a final top position. See if it really does end up being different from our estimate.
     // clearFloatsIfNeeded can also mark the child as needing a layout even though we didn't move. This happens
     // when collapseMargins dynamically adds overhanging floats because of a child with negative margins.
     if (logicalTopAfterClear != logicalTopEstimate || child.needsLayout() || (paginated && childBlockFlow && childBlockFlow->shouldBreakAtLineToAvoidWidow())) {
         if (child.shrinkToAvoidFloats()) {
             // The child's width depends on the line width.
             // When the child shifts to clear an item, its width can
             // change (because it has more available line width).
             // So go ahead and mark the item as dirty.
             child.setChildNeedsLayout(MarkOnlyThis);
         }

         if (childBlockFlow) {
             if (!child.avoidsFloats() && childBlockFlow->containsFloats())
                 childBlockFlow->markAllDescendantsWithFloatsForLayout();
             if (!child.needsLayout())
                 child.markForPaginationRelayoutIfNeeded();
         }

         // Our guess was wrong. Make the child lay itself out again.
         child.layoutIfNeeded();
     }

     if (updateRegionRangeForBoxChild(child)) {
         child.setNeedsLayout(MarkOnlyThis);
         child.layoutIfNeeded();
     }

     // We are no longer at the top of the block if we encounter a non-empty child.
     // This has to be done after checking for clear, so that margins can be reset if a clear occurred.
     if (marginInfo.atBeforeSideOfBlock() && !child.isSelfCollapsingBlock())
         marginInfo.setAtBeforeSideOfBlock(false);

     // Now place the child in the correct left position
     determineLogicalLeftPositionForChild(child, ApplyLayoutDelta);

     LayoutSize childOffset = child.location() - oldRect.location();
 #if ENABLE(CSS_SHAPES)
     relayoutShapeDescendantIfMoved(child.isRenderBlock() ? toRenderBlock(&child) : nullptr, childOffset);
 #endif

     // Update our height now that the child has been placed in the correct position.
     setLogicalHeight(logicalHeight() + logicalHeightForChild(child));
     if (mustSeparateMarginAfterForChild(child)) {
         setLogicalHeight(logicalHeight() + marginAfterForChild(child));
         marginInfo.clearMargin();
     }
     // If the child has overhanging floats that intrude into following siblings (or possibly out
     // of this block), then the parent gets notified of the floats now.
     if (childBlockFlow && childBlockFlow->containsFloats())
         maxFloatLogicalBottom = max(maxFloatLogicalBottom, addOverhangingFloats(*childBlockFlow, !childNeededLayout));

     if (childOffset.width() || childOffset.height()) {
         view().addLayoutDelta(childOffset);

         // If the child moved, we have to repaint it as well as any floating/positioned
         // descendants. An exception is if we need a layout. In this case, we know we're going to
         // repaint ourselves (and the child) anyway.
         if (childHadLayout && !selfNeedsLayout() && child.checkForRepaintDuringLayout())
             child.repaintDuringLayoutIfMoved(oldRect);
     }

     if (!childHadLayout && child.checkForRepaintDuringLayout()) {
         child.repaint();
         child.repaintOverhangingFloats(true);
     }

     if (paginated) {
         // Check for an after page/column break.
         LayoutUnit newHeight = applyAfterBreak(child, logicalHeight(), marginInfo);
         if (newHeight != height())
             setLogicalHeight(newHeight);
     }

     ASSERT(view().layoutDeltaMatches(oldLayoutDelta));
 }

 void RenderBlockFlow::adjustPositionedBlock(RenderBox& child, const MarginInfo& marginInfo)
 {
     bool isHorizontal = isHorizontalWritingMode();
     bool hasStaticBlockPosition = child.style().hasStaticBlockPosition(isHorizontal);

     LayoutUnit logicalTop = logicalHeight();
     updateStaticInlinePositionForChild(child, logicalTop);

     if (!marginInfo.canCollapseWithMarginBefore()) {
         // Positioned blocks don't collapse margins, so add the margin provided by
         // the container now. The child's own margin is added later when calculating its logical top.
         LayoutUnit collapsedBeforePos = marginInfo.positiveMargin();
         LayoutUnit collapsedBeforeNeg = marginInfo.negativeMargin();
         logicalTop += collapsedBeforePos - collapsedBeforeNeg;
     }

     RenderLayer* childLayer = child.layer();
     if (childLayer->staticBlockPosition() != logicalTop) {
         childLayer->setStaticBlockPosition(logicalTop);
         if (hasStaticBlockPosition)
             child.setChildNeedsLayout(MarkOnlyThis);
     }
 }

 void RenderBlockFlow::adjustFloatingBlock(const MarginInfo& marginInfo)
 {
     // The float should be positioned taking into account the bottom margin
     // of the previous flow. We add that margin into the height, get the
     // float positioned properly, and then subtract the margin out of the
     // height again. In the case of self-collapsing blocks, we always just
     // use the top margins, since the self-collapsing block collapsed its
     // own bottom margin into its top margin.
     //
     // Note also that the previous flow may collapse its margin into the top of
     // our block. If this is the case, then we do not add the margin in to our
     // height when computing the position of the float. This condition can be tested
     // for by simply calling canCollapseWithMarginBefore. See
     // http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/046.html for
     // an example of this scenario.
     LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? LayoutUnit() : marginInfo.margin();
     setLogicalHeight(logicalHeight() + marginOffset);
     positionNewFloats();
     setLogicalHeight(logicalHeight() - marginOffset);
 }

 void RenderBlockFlow::updateStaticInlinePositionForChild(RenderBox& child, LayoutUnit logicalTop)
 {
     if (child.style().isOriginalDisplayInlineType())
         setStaticInlinePositionForChild(child, logicalTop, startAlignedOffsetForLine(logicalTop, false));
     else
         setStaticInlinePositionForChild(child, logicalTop, startOffsetForContent(logicalTop));
 }

 void RenderBlockFlow::setStaticInlinePositionForChild(RenderBox& child, LayoutUnit blockOffset, LayoutUnit inlinePosition)
 {
     if (flowThreadContainingBlock()) {
         // Shift the inline position to exclude the region offset.
         inlinePosition += startOffsetForContent() - startOffsetForContent(blockOffset);
     }
     child.layer()->setStaticInlinePosition(inlinePosition);
 }

 RenderBlockFlow::MarginValues RenderBlockFlow::marginValuesForChild(RenderBox& child) const
 {
     LayoutUnit childBeforePositive = 0;
     LayoutUnit childBeforeNegative = 0;
     LayoutUnit childAfterPositive = 0;
     LayoutUnit childAfterNegative = 0;

     LayoutUnit beforeMargin = 0;
     LayoutUnit afterMargin = 0;

     RenderBlockFlow* childRenderBlock = child.isRenderBlockFlow() ? toRenderBlockFlow(&child) : nullptr;

     // If the child has the same directionality as we do, then we can just return its
     // margins in the same direction.
     if (!child.isWritingModeRoot()) {
         if (childRenderBlock) {
             childBeforePositive = childRenderBlock->maxPositiveMarginBefore();
             childBeforeNegative = childRenderBlock->maxNegativeMarginBefore();
             childAfterPositive = childRenderBlock->maxPositiveMarginAfter();
             childAfterNegative = childRenderBlock->maxNegativeMarginAfter();
         } else {
             beforeMargin = child.marginBefore();
             afterMargin = child.marginAfter();
         }
     } else if (child.isHorizontalWritingMode() == isHorizontalWritingMode()) {
         // The child has a different directionality. If the child is parallel, then it's just
         // flipped relative to us. We can use the margins for the opposite edges.
         if (childRenderBlock) {
             childBeforePositive = childRenderBlock->maxPositiveMarginAfter();
             childBeforeNegative = childRenderBlock->maxNegativeMarginAfter();
             childAfterPositive = childRenderBlock->maxPositiveMarginBefore();
             childAfterNegative = childRenderBlock->maxNegativeMarginBefore();
         } else {
             beforeMargin = child.marginAfter();
             afterMargin = child.marginBefore();
         }
     } else {
         // The child is perpendicular to us, which means its margins don't collapse but are on the
         // "logical left/right" sides of the child box. We can just return the raw margin in this case.
         beforeMargin = marginBeforeForChild(child);
         afterMargin = marginAfterForChild(child);
     }

     // Resolve uncollapsing margins into their positive/negative buckets.
     if (beforeMargin) {
         if (beforeMargin > 0)
             childBeforePositive = beforeMargin;
         else
             childBeforeNegative = -beforeMargin;
     }
     if (afterMargin) {
         if (afterMargin > 0)
             childAfterPositive = afterMargin;
         else
             childAfterNegative = -afterMargin;
     }

     return MarginValues(childBeforePositive, childBeforeNegative, childAfterPositive, childAfterNegative);
 }

 LayoutUnit RenderBlockFlow::collapseMargins(RenderBox& child, MarginInfo& marginInfo)
 {
     bool childDiscardMarginBefore = mustDiscardMarginBeforeForChild(child);
     bool childDiscardMarginAfter = mustDiscardMarginAfterForChild(child);
     bool childIsSelfCollapsing = child.isSelfCollapsingBlock();

     // The child discards the before margin when the the after margin has discard in the case of a self collapsing block.
     childDiscardMarginBefore = childDiscardMarginBefore || (childDiscardMarginAfter && childIsSelfCollapsing);

     // Get the four margin values for the child and cache them.
     const MarginValues childMargins = marginValuesForChild(child);

     // Get our max pos and neg top margins.
     LayoutUnit posTop = childMargins.positiveMarginBefore();
     LayoutUnit negTop = childMargins.negativeMarginBefore();

     // For self-collapsing blocks, collapse our bottom margins into our
     // top to get new posTop and negTop values.
     if (childIsSelfCollapsing) {
         posTop = max(posTop, childMargins.positiveMarginAfter());
         negTop = max(negTop, childMargins.negativeMarginAfter());
     }

     // See if the top margin is quirky. We only care if this child has
     // margins that will collapse with us.
     bool topQuirk = hasMarginBeforeQuirk(child);

     if (marginInfo.canCollapseWithMarginBefore()) {
         if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
             // This child is collapsing with the top of the
             // block. If it has larger margin values, then we need to update
             // our own maximal values.
             if (!document().inQuirksMode() || !marginInfo.quirkContainer() || !topQuirk)
                 setMaxMarginBeforeValues(max(posTop, maxPositiveMarginBefore()), max(negTop, maxNegativeMarginBefore()));

             // The minute any of the margins involved isn't a quirk, don't
             // collapse it away, even if the margin is smaller (www.webreference.com
             // has an example of this, a <dt> with 0.8em author-specified inside
             // a <dl> inside a <td>.
             if (!marginInfo.determinedMarginBeforeQuirk() && !topQuirk && (posTop - negTop)) {
                 setHasMarginBeforeQuirk(false);
                 marginInfo.setDeterminedMarginBeforeQuirk(true);
             }

             if (!marginInfo.determinedMarginBeforeQuirk() && topQuirk && !marginBefore())
                 // We have no top margin and our top child has a quirky margin.
                 // We will pick up this quirky margin and pass it through.
                 // This deals with the <td><div><p> case.
                 // Don't do this for a block that split two inlines though. You do
                 // still apply margins in this case.
                 setHasMarginBeforeQuirk(true);
         } else
             // The before margin of the container will also discard all the margins it is collapsing with.
             setMustDiscardMarginBefore();
     }

     // Once we find a child with discardMarginBefore all the margins collapsing with us must also discard.
     if (childDiscardMarginBefore) {
         marginInfo.setDiscardMargin(true);
         marginInfo.clearMargin();
     }

     if (marginInfo.quirkContainer() && marginInfo.atBeforeSideOfBlock() && (posTop - negTop))
         marginInfo.setHasMarginBeforeQuirk(topQuirk);

     LayoutUnit beforeCollapseLogicalTop = logicalHeight();
     LayoutUnit logicalTop = beforeCollapseLogicalTop;
     if (childIsSelfCollapsing) {
         // For a self collapsing block both the before and after margins get discarded. The block doesn't contribute anything to the height of the block.
         // Also, the child's top position equals the logical height of the container.
         if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
             // This child has no height. We need to compute our
             // position before we collapse the child's margins together,
             // so that we can get an accurate position for the zero-height block.
             LayoutUnit collapsedBeforePos = max(marginInfo.positiveMargin(), childMargins.positiveMarginBefore());
             LayoutUnit collapsedBeforeNeg = max(marginInfo.negativeMargin(), childMargins.negativeMarginBefore());
             marginInfo.setMargin(collapsedBeforePos, collapsedBeforeNeg);

             // Now collapse the child's margins together, which means examining our
             // bottom margin values as well.
             marginInfo.setPositiveMarginIfLarger(childMargins.positiveMarginAfter());
             marginInfo.setNegativeMarginIfLarger(childMargins.negativeMarginAfter());

             if (!marginInfo.canCollapseWithMarginBefore())
                 // We need to make sure that the position of the self-collapsing block
                 // is correct, since it could have overflowing content
                 // that needs to be positioned correctly (e.g., a block that
                 // had a specified height of 0 but that actually had subcontent).
                 logicalTop = logicalHeight() + collapsedBeforePos - collapsedBeforeNeg;
         }
     } else {
         if (mustSeparateMarginBeforeForChild(child)) {
             ASSERT(!marginInfo.discardMargin() || (marginInfo.discardMargin() && !marginInfo.margin()));
             // If we are at the before side of the block and we collapse, ignore the computed margin
             // and just add the child margin to the container height. This will correctly position
             // the child inside the container.
             LayoutUnit separateMargin = !marginInfo.canCollapseWithMarginBefore() ? marginInfo.margin() : LayoutUnit(0);
             setLogicalHeight(logicalHeight() + separateMargin + marginBeforeForChild(child));
             logicalTop = logicalHeight();
         } else if (!marginInfo.discardMargin() && (!marginInfo.atBeforeSideOfBlock()
             || (!marginInfo.canCollapseMarginBeforeWithChildren()
             && (!document().inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.hasMarginBeforeQuirk())))) {
             // We're collapsing with a previous sibling's margins and not
             // with the top of the block.
             setLogicalHeight(logicalHeight() + max(marginInfo.positiveMargin(), posTop) - max(marginInfo.negativeMargin(), negTop));
             logicalTop = logicalHeight();
         }

         marginInfo.setDiscardMargin(childDiscardMarginAfter);

         if (!marginInfo.discardMargin()) {
             marginInfo.setPositiveMargin(childMargins.positiveMarginAfter());
             marginInfo.setNegativeMargin(childMargins.negativeMarginAfter());
         } else
             marginInfo.clearMargin();

         if (marginInfo.margin())
             marginInfo.setHasMarginAfterQuirk(hasMarginAfterQuirk(child));
     }

     // If margins would pull us past the top of the next page, then we need to pull back and pretend like the margins
     // collapsed into the page edge.
     LayoutState* layoutState = view().layoutState();
     if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop
         && hasNextPage(beforeCollapseLogicalTop)) {
         LayoutUnit oldLogicalTop = logicalTop;
         logicalTop = min(logicalTop, nextPageLogicalTop(beforeCollapseLogicalTop));
         setLogicalHeight(logicalHeight() + (logicalTop - oldLogicalTop));
     }

     // If we have collapsed into a previous sibling and so reduced the height of the parent, ensure any floats that now
     // overhang from the previous sibling are added to our parent. If the child's previous sibling itself is a float the child will avoid
     // or clear it anyway, so don't worry about any floating children it may contain.
     LayoutUnit oldLogicalHeight = logicalHeight();
     setLogicalHeight(logicalTop);
     RenderObject* prev = child.previousSibling();
     if (prev && prev->isRenderBlockFlow() && !prev->isFloatingOrOutOfFlowPositioned()) {
         RenderBlockFlow& block = toRenderBlockFlow(*prev);
         if (block.containsFloats() && !block.avoidsFloats() && (block.logicalTop() + block.lowestFloatLogicalBottom()) > logicalTop)
             addOverhangingFloats(block, false);
     }
     setLogicalHeight(oldLogicalHeight);

     return logicalTop;
 }

 LayoutUnit RenderBlockFlow::clearFloatsIfNeeded(RenderBox& child, MarginInfo& marginInfo, LayoutUnit oldTopPosMargin, LayoutUnit oldTopNegMargin, LayoutUnit yPos)
 {
     LayoutUnit heightIncrease = getClearDelta(child, yPos);
     if (!heightIncrease)
         return yPos;

     if (child.isSelfCollapsingBlock()) {
         bool childDiscardMargin = mustDiscardMarginBeforeForChild(child) || mustDiscardMarginAfterForChild(child);

         // For self-collapsing blocks that clear, they can still collapse their
         // margins with following siblings. Reset the current margins to represent
         // the self-collapsing block's margins only.
         // If DISCARD is specified for -webkit-margin-collapse, reset the margin values.
         if (!childDiscardMargin) {
             MarginValues childMargins = marginValuesForChild(child);
             marginInfo.setPositiveMargin(max(childMargins.positiveMarginBefore(), childMargins.positiveMarginAfter()));
             marginInfo.setNegativeMargin(max(childMargins.negativeMarginBefore(), childMargins.negativeMarginAfter()));
         } else
             marginInfo.clearMargin();
         marginInfo.setDiscardMargin(childDiscardMargin);

         // CSS2.1 states:
         // "If the top and bottom margins of an element with clearance are adjoining, its margins collapse with
         // the adjoining margins of following siblings but that resulting margin does not collapse with the bottom margin of the parent block."
         // So the parent's bottom margin cannot collapse through this block or any subsequent self-collapsing blocks. Check subsequent siblings
         // for a block with height - if none is found then don't allow the margins to collapse with the parent.
         bool wouldCollapseMarginsWithParent = marginInfo.canCollapseMarginAfterWithChildren();
         for (RenderBox* curr = child.nextSiblingBox(); curr && wouldCollapseMarginsWithParent; curr = curr->nextSiblingBox()) {
             if (!curr->isFloatingOrOutOfFlowPositioned() && !curr->isSelfCollapsingBlock())
                 wouldCollapseMarginsWithParent = false;
         }
         if (wouldCollapseMarginsWithParent)
             marginInfo.setCanCollapseMarginAfterWithChildren(false);

         // CSS2.1: "the amount of clearance is set so that clearance + margin-top = [height of float], i.e., clearance = [height of float] - margin-top"
         // Move the top of the child box to the bottom of the float ignoring the child's top margin.
         LayoutUnit collapsedMargin = collapsedMarginBeforeForChild(child);
         setLogicalHeight(child.logicalTop() - collapsedMargin);
         // A negative collapsed margin-top value cancels itself out as it has already been factored into |yPos| above.
         heightIncrease -= max(LayoutUnit(), collapsedMargin);
     } else
         // Increase our height by the amount we had to clear.
         setLogicalHeight(logicalHeight() + heightIncrease);

     if (marginInfo.canCollapseWithMarginBefore()) {
         // We can no longer collapse with the top of the block since a clear
         // occurred. The empty blocks collapse into the cleared block.
         // FIXME: This isn't quite correct. Need clarification for what to do
         // if the height the cleared block is offset by is smaller than the
         // margins involved.
         setMaxMarginBeforeValues(oldTopPosMargin, oldTopNegMargin);
         marginInfo.setAtBeforeSideOfBlock(false);

         // In case the child discarded the before margin of the block we need to reset the mustDiscardMarginBefore flag to the initial value.
         setMustDiscardMarginBefore(style().marginBeforeCollapse() == MDISCARD);
     }

     LayoutUnit logicalTop = yPos + heightIncrease;
     // After margin collapsing, one of our floats may now intrude into the child. If the child doesn't contain floats of its own it
     // won't get picked up for relayout even though the logical top estimate was wrong - so add the newly intruding float now.
     if (containsFloats() && child.isRenderBlockFlow() && !toRenderBlockFlow(child).containsFloats() && !child.avoidsFloats() && lowestFloatLogicalBottom() > logicalTop)
         toRenderBlockFlow(child).addIntrudingFloats(this, logicalLeftOffsetForContent(), logicalTop);

     return logicalTop;
 }

 void RenderBlockFlow::marginBeforeEstimateForChild(RenderBox& child, LayoutUnit& positiveMarginBefore, LayoutUnit& negativeMarginBefore, bool& discardMarginBefore) const
 {
     // Give up if in quirks mode and we're a body/table cell and the top margin of the child box is quirky.
     // Give up if the child specified -webkit-margin-collapse: separate that prevents collapsing.
     // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
     if ((document().inQuirksMode() && hasMarginAfterQuirk(child) && (isTableCell() || isBody())) || child.style().marginBeforeCollapse() == MSEPARATE)
         return;

     // The margins are discarded by a child that specified -webkit-margin-collapse: discard.
     // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
     if (child.style().marginBeforeCollapse() == MDISCARD) {
         positiveMarginBefore = 0;
         negativeMarginBefore = 0;
         discardMarginBefore = true;
         return;
     }

     LayoutUnit beforeChildMargin = marginBeforeForChild(child);
     positiveMarginBefore = max(positiveMarginBefore, beforeChildMargin);
     negativeMarginBefore = max(negativeMarginBefore, -beforeChildMargin);

     if (!child.isRenderBlockFlow())
         return;

     RenderBlockFlow& childBlock = toRenderBlockFlow(child);
     if (childBlock.childrenInline() || childBlock.isWritingModeRoot())
         return;

     MarginInfo childMarginInfo(childBlock, childBlock.borderAndPaddingBefore(), childBlock.borderAndPaddingAfter());
     if (!childMarginInfo.canCollapseMarginBeforeWithChildren())
         return;

     RenderBox* grandchildBox = childBlock.firstChildBox();
     for (; grandchildBox; grandchildBox = grandchildBox->nextSiblingBox()) {
         if (!grandchildBox->isFloatingOrOutOfFlowPositioned())
             break;
     }

     // Give up if there is clearance on the box, since it probably won't collapse into us.
     if (!grandchildBox || grandchildBox->style().clear() != CNONE)
         return;

     // Make sure to update the block margins now for the grandchild box so that we're looking at current values.
     if (grandchildBox->needsLayout()) {
         grandchildBox->computeAndSetBlockDirectionMargins(this);
         if (grandchildBox->isRenderBlock()) {
             RenderBlock* grandchildBlock = toRenderBlock(grandchildBox);
             grandchildBlock->setHasMarginBeforeQuirk(grandchildBox->style().hasMarginBeforeQuirk());
             grandchildBlock->setHasMarginAfterQuirk(grandchildBox->style().hasMarginAfterQuirk());
         }
     }

     // Collapse the margin of the grandchild box with our own to produce an estimate.
     childBlock.marginBeforeEstimateForChild(*grandchildBox, positiveMarginBefore, negativeMarginBefore, discardMarginBefore);
 }

 LayoutUnit RenderBlockFlow::estimateLogicalTopPosition(RenderBox& child, const MarginInfo& marginInfo, LayoutUnit& estimateWithoutPagination)
 {
     // FIXME: We need to eliminate the estimation of vertical position, because when it's wrong we sometimes trigger a pathological
     // relayout if there are intruding floats.
     LayoutUnit logicalTopEstimate = logicalHeight();
     if (!marginInfo.canCollapseWithMarginBefore()) {
         LayoutUnit positiveMarginBefore = 0;
         LayoutUnit negativeMarginBefore = 0;
         bool discardMarginBefore = false;
         if (child.selfNeedsLayout()) {
             // Try to do a basic estimation of how the collapse is going to go.
             marginBeforeEstimateForChild(child, positiveMarginBefore, negativeMarginBefore, discardMarginBefore);
         } else {
             // Use the cached collapsed margin values from a previous layout. Most of the time they
             // will be right.
             MarginValues marginValues = marginValuesForChild(child);
             positiveMarginBefore = max(positiveMarginBefore, marginValues.positiveMarginBefore());
             negativeMarginBefore = max(negativeMarginBefore, marginValues.negativeMarginBefore());
             discardMarginBefore = mustDiscardMarginBeforeForChild(child);
         }

         // Collapse the result with our current margins.
         if (!discardMarginBefore)
             logicalTopEstimate += max(marginInfo.positiveMargin(), positiveMarginBefore) - max(marginInfo.negativeMargin(), negativeMarginBefore);
     }

     // Adjust logicalTopEstimate down to the next page if the margins are so large that we don't fit on the current
     // page.
     LayoutState* layoutState = view().layoutState();
     if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight()
         && hasNextPage(logicalHeight()))
         logicalTopEstimate = min(logicalTopEstimate, nextPageLogicalTop(logicalHeight()));

     logicalTopEstimate += getClearDelta(child, logicalTopEstimate);

     estimateWithoutPagination = logicalTopEstimate;

     if (layoutState->isPaginated()) {
         // If the object has a page or column break value of "before", then we should shift to the top of the next page.
         logicalTopEstimate = applyBeforeBreak(child, logicalTopEstimate);

         // For replaced elements and scrolled elements, we want to shift them to the next page if they don't fit on the current one.
         logicalTopEstimate = adjustForUnsplittableChild(child, logicalTopEstimate);

         if (!child.selfNeedsLayout() && child.isRenderBlock())
             logicalTopEstimate += toRenderBlock(child).paginationStrut();
     }

     return logicalTopEstimate;
 }

 void RenderBlockFlow::setCollapsedBottomMargin(const MarginInfo& marginInfo)
 {
     if (marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()) {
         // Update the after side margin of the container to discard if the after margin of the last child also discards and we collapse with it.
         // Don't update the max margin values because we won't need them anyway.
         if (marginInfo.discardMargin()) {
             setMustDiscardMarginAfter();
             return;
         }

         // Update our max pos/neg bottom margins, since we collapsed our bottom margins
         // with our children.
         setMaxMarginAfterValues(max(maxPositiveMarginAfter(), marginInfo.positiveMargin()), max(maxNegativeMarginAfter(), marginInfo.negativeMargin()));

         if (!marginInfo.hasMarginAfterQuirk())
             setHasMarginAfterQuirk(false);

         if (marginInfo.hasMarginAfterQuirk() && !marginAfter())
             // We have no bottom margin and our last child has a quirky margin.
             // We will pick up this quirky margin and pass it through.
             // This deals with the <td><div><p> case.
             setHasMarginAfterQuirk(true);
     }
 }

 void RenderBlockFlow::handleAfterSideOfBlock(LayoutUnit beforeSide, LayoutUnit afterSide, MarginInfo& marginInfo)
 {
     marginInfo.setAtAfterSideOfBlock(true);

     // If we can't collapse with children then go ahead and add in the bottom margin.
     if (!marginInfo.discardMargin() && (!marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()
         && (!document().inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.hasMarginAfterQuirk())))
         setLogicalHeight(logicalHeight() + marginInfo.margin());

     // Now add in our bottom border/padding.
     setLogicalHeight(logicalHeight() + afterSide);

     // Negative margins can cause our height to shrink below our minimal height (border/padding).
     // If this happens, ensure that the computed height is increased to the minimal height.
     setLogicalHeight(max(logicalHeight(), beforeSide + afterSide));

     // Update our bottom collapsed margin info.
     setCollapsedBottomMargin(marginInfo);
 }

 void RenderBlockFlow::setMaxMarginBeforeValues(LayoutUnit pos, LayoutUnit neg)
 {
     if (!m_rareData) {
         if (pos == RenderBlockFlowRareData::positiveMarginBeforeDefault(*this) && neg == RenderBlockFlowRareData::negativeMarginBeforeDefault(*this))
             return;
         m_rareData = adoptPtr(new RenderBlockFlowRareData(*this));
     }
     m_rareData->m_margins.setPositiveMarginBefore(pos);
     m_rareData->m_margins.setNegativeMarginBefore(neg);
 }

 void RenderBlockFlow::setMaxMarginAfterValues(LayoutUnit pos, LayoutUnit neg)
 {
     if (!m_rareData) {
         if (pos == RenderBlockFlowRareData::positiveMarginAfterDefault(*this) && neg == RenderBlockFlowRareData::negativeMarginAfterDefault(*this))
             return;
         m_rareData = adoptPtr(new RenderBlockFlowRareData(*this));
     }
     m_rareData->m_margins.setPositiveMarginAfter(pos);
     m_rareData->m_margins.setNegativeMarginAfter(neg);
 }

 void RenderBlockFlow::setMustDiscardMarginBefore(bool value)
 {
     if (style().marginBeforeCollapse() == MDISCARD) {
         ASSERT(value);
         return;
     }

     if (!m_rareData && !value)
         return;

     if (!m_rareData)
         m_rareData = adoptPtr(new RenderBlockFlowRareData(*this));

     m_rareData->m_discardMarginBefore = value;
 }

 void RenderBlockFlow::setMustDiscardMarginAfter(bool value)
 {
     if (style().marginAfterCollapse() == MDISCARD) {
         ASSERT(value);
         return;
     }

     if (!m_rareData && !value)
         return;

     if (!m_rareData)
         m_rareData = adoptPtr(new RenderBlockFlowRareData(*this));

     m_rareData->m_discardMarginAfter = value;
 }

 bool RenderBlockFlow::mustDiscardMarginBefore() const
 {
     return style().marginBeforeCollapse() == MDISCARD || (m_rareData && m_rareData->m_discardMarginBefore);
 }

 bool RenderBlockFlow::mustDiscardMarginAfter() const
 {
     return style().marginAfterCollapse() == MDISCARD || (m_rareData && m_rareData->m_discardMarginAfter);
 }

 bool RenderBlockFlow::mustDiscardMarginBeforeForChild(const RenderBox& child) const
 {
     ASSERT(!child.selfNeedsLayout());
     if (!child.isWritingModeRoot())
         return child.isRenderBlockFlow() ? toRenderBlockFlow(child).mustDiscardMarginBefore() : (child.style().marginBeforeCollapse() == MDISCARD);
     if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
         return child.isRenderBlockFlow() ? toRenderBlockFlow(child).mustDiscardMarginAfter() : (child.style().marginAfterCollapse() == MDISCARD);

     // FIXME: We return false here because the implementation is not geometrically complete. We have values only for before/after, not start/end.
     // In case the boxes are perpendicular we assume the property is not specified.
     return false;
 }

 bool RenderBlockFlow::mustDiscardMarginAfterForChild(const RenderBox& child) const
 {
     ASSERT(!child.selfNeedsLayout());
     if (!child.isWritingModeRoot())
         return child.isRenderBlockFlow() ? toRenderBlockFlow(child).mustDiscardMarginAfter() : (child.style().marginAfterCollapse() == MDISCARD);
     if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
         return child.isRenderBlockFlow() ? toRenderBlockFlow(child).mustDiscardMarginBefore() : (child.style().marginBeforeCollapse() == MDISCARD);

     // FIXME: See |mustDiscardMarginBeforeForChild| above.
     return false;
 }

 bool RenderBlockFlow::mustSeparateMarginBeforeForChild(const RenderBox& child) const
 {
     ASSERT(!child.selfNeedsLayout());
     const RenderStyle& childStyle = child.style();
     if (!child.isWritingModeRoot())
         return childStyle.marginBeforeCollapse() == MSEPARATE;
     if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
         return childStyle.marginAfterCollapse() == MSEPARATE;

     // FIXME: See |mustDiscardMarginBeforeForChild| above.
     return false;
 }

 bool RenderBlockFlow::mustSeparateMarginAfterForChild(const RenderBox& child) const
 {
     ASSERT(!child.selfNeedsLayout());
     const RenderStyle& childStyle = child.style();
     if (!child.isWritingModeRoot())
         return childStyle.marginAfterCollapse() == MSEPARATE;
     if (child.isHorizontalWritingMode() == isHorizontalWritingMode())
         return childStyle.marginBeforeCollapse() == MSEPARATE;

     // FIXME: See |mustDiscardMarginBeforeForChild| above.
     return false;
 }

 static bool inNormalFlow(RenderBox& child)
 {
     RenderBlock* curr = child.containingBlock();
     while (curr && curr != &child.view()) {
         if (curr->hasColumns() || curr->isRenderFlowThread())
             return true;
         if (curr->isFloatingOrOutOfFlowPositioned())
             return false;
         curr = curr->containingBlock();
     }
     return true;
 }

 LayoutUnit RenderBlockFlow::applyBeforeBreak(RenderBox& child, LayoutUnit logicalOffset)
 {
     // FIXME: Add page break checking here when we support printing.
     bool checkColumnBreaks = view().layoutState()->isPaginatingColumns();
     bool checkPageBreaks = !checkColumnBreaks && view().layoutState()->m_pageLogicalHeight; // FIXME: Once columns can print we have to check this.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     bool checkRegionBreaks = flowThread && flowThread->isRenderNamedFlowThread();
     bool checkBeforeAlways = (checkColumnBreaks && child.style().columnBreakBefore() == PBALWAYS) || (checkPageBreaks && child.style().pageBreakBefore() == PBALWAYS)
         || (checkRegionBreaks && child.style().regionBreakBefore() == PBALWAYS);
     if (checkBeforeAlways && inNormalFlow(child) && hasNextPage(logicalOffset, IncludePageBoundary)) {
         if (checkColumnBreaks)
             view().layoutState()->addForcedColumnBreak(&child, logicalOffset);
         if (checkRegionBreaks) {
             LayoutUnit offsetBreakAdjustment = 0;
             if (flowThread->addForcedRegionBreak(this, offsetFromLogicalTopOfFirstPage() + logicalOffset, &child, true, &offsetBreakAdjustment))
                 return logicalOffset + offsetBreakAdjustment;
         }
         return nextPageLogicalTop(logicalOffset, IncludePageBoundary);
     }
     return logicalOffset;
 }

 LayoutUnit RenderBlockFlow::applyAfterBreak(RenderBox& child, LayoutUnit logicalOffset, MarginInfo& marginInfo)
 {
     // FIXME: Add page break checking here when we support printing.
     bool checkColumnBreaks = view().layoutState()->isPaginatingColumns();
     bool checkPageBreaks = !checkColumnBreaks && view().layoutState()->m_pageLogicalHeight; // FIXME: Once columns can print we have to check this.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     bool checkRegionBreaks = flowThread && flowThread->isRenderNamedFlowThread();
     bool checkAfterAlways = (checkColumnBreaks && child.style().columnBreakAfter() == PBALWAYS) || (checkPageBreaks && child.style().pageBreakAfter() == PBALWAYS)
         || (checkRegionBreaks && child.style().regionBreakAfter() == PBALWAYS);
     if (checkAfterAlways && inNormalFlow(child) && hasNextPage(logicalOffset, IncludePageBoundary)) {
         LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? LayoutUnit() : marginInfo.margin();

         // So our margin doesn't participate in the next collapsing steps.
         marginInfo.clearMargin();

         if (checkColumnBreaks)
             view().layoutState()->addForcedColumnBreak(&child, logicalOffset);
         if (checkRegionBreaks) {
             LayoutUnit offsetBreakAdjustment = 0;
             if (flowThread->addForcedRegionBreak(this, offsetFromLogicalTopOfFirstPage() + logicalOffset + marginOffset, &child, false, &offsetBreakAdjustment))
                 return logicalOffset + marginOffset + offsetBreakAdjustment;
         }
         return nextPageLogicalTop(logicalOffset, IncludePageBoundary);
     }
     return logicalOffset;
 }

 LayoutUnit RenderBlockFlow::adjustBlockChildForPagination(LayoutUnit logicalTopAfterClear, LayoutUnit estimateWithoutPagination, RenderBox& child, bool atBeforeSideOfBlock)
 {
     RenderBlock* childRenderBlock = child.isRenderBlock() ? toRenderBlock(&child) : nullptr;

     if (estimateWithoutPagination != logicalTopAfterClear) {
         // Our guess prior to pagination movement was wrong. Before we attempt to paginate, let's try again at the new
         // position.
         setLogicalHeight(logicalTopAfterClear);
         setLogicalTopForChild(child, logicalTopAfterClear, ApplyLayoutDelta);

         if (child.shrinkToAvoidFloats()) {
             // The child's width depends on the line width.
             // When the child shifts to clear an item, its width can
             // change (because it has more available line width).
             // So go ahead and mark the item as dirty.
             child.setChildNeedsLayout(MarkOnlyThis);
         }

         if (childRenderBlock) {
             if (!child.avoidsFloats() && childRenderBlock->containsFloats())
                 toRenderBlockFlow(childRenderBlock)->markAllDescendantsWithFloatsForLayout();
             if (!child.needsLayout())
                 child.markForPaginationRelayoutIfNeeded();
         }

         // Our guess was wrong. Make the child lay itself out again.
         child.layoutIfNeeded();
     }

     LayoutUnit oldTop = logicalTopAfterClear;

     // If the object has a page or column break value of "before", then we should shift to the top of the next page.
     LayoutUnit result = applyBeforeBreak(child, logicalTopAfterClear);

     if (pageLogicalHeightForOffset(result)) {
         LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(result, ExcludePageBoundary);
         LayoutUnit spaceShortage = child.logicalHeight() - remainingLogicalHeight;
         if (spaceShortage > 0) {
             // If the child crosses a column boundary, report a break, in case nothing inside it has already
             // done so. The column balancer needs to know how much it has to stretch the columns to make more
             // content fit. If no breaks are reported (but do occur), the balancer will have no clue. FIXME:
             // This should be improved, though, because here we just pretend that the child is
             // unsplittable. A splittable child, on the other hand, has break opportunities at every position
             // where there's no child content, border or padding. In other words, we risk stretching more
             // than necessary.
             setPageBreak(result, spaceShortage);
         }
     }

     // For replaced elements and scrolled elements, we want to shift them to the next page if they don't fit on the current one.
     LayoutUnit logicalTopBeforeUnsplittableAdjustment = result;
     LayoutUnit logicalTopAfterUnsplittableAdjustment = adjustForUnsplittableChild(child, result);

     LayoutUnit paginationStrut = 0;
     LayoutUnit unsplittableAdjustmentDelta = logicalTopAfterUnsplittableAdjustment - logicalTopBeforeUnsplittableAdjustment;
     if (unsplittableAdjustmentDelta)
         paginationStrut = unsplittableAdjustmentDelta;
     else if (childRenderBlock && childRenderBlock->paginationStrut())
         paginationStrut = childRenderBlock->paginationStrut();

     if (paginationStrut) {
         // We are willing to propagate out to our parent block as long as we were at the top of the block prior
         // to collapsing our margins, and as long as we didn't clear or move as a result of other pagination.
         if (atBeforeSideOfBlock && oldTop == result && !isOutOfFlowPositioned() && !isTableCell()) {
             // FIXME: Should really check if we're exceeding the page height before propagating the strut, but we don't
             // have all the information to do so (the strut only has the remaining amount to push). Gecko gets this wrong too
             // and pushes to the next page anyway, so not too concerned about it.
             setPaginationStrut(result + paginationStrut);
             if (childRenderBlock)
                 childRenderBlock->setPaginationStrut(0);
         } else
             result += paginationStrut;
     }

     // Similar to how we apply clearance. Go ahead and boost height() to be the place where we're going to position the child.
     setLogicalHeight(logicalHeight() + (result - oldTop));

     // Return the final adjusted logical top.
     return result;
 }

 static inline LayoutUnit calculateMinimumPageHeight(RenderStyle* renderStyle, RootInlineBox* lastLine, LayoutUnit lineTop, LayoutUnit lineBottom)
 {
     // We may require a certain minimum number of lines per page in order to satisfy
     // orphans and widows, and that may affect the minimum page height.
     unsigned lineCount = max<unsigned>(renderStyle->hasAutoOrphans() ? 1 : renderStyle->orphans(), renderStyle->hasAutoWidows() ? 1 : renderStyle->widows());
     if (lineCount > 1) {
         RootInlineBox* line = lastLine;
         for (unsigned i = 1; i < lineCount && line->prevRootBox(); i++)
             line = line->prevRootBox();

         // FIXME: Paginating using line overflow isn't all fine. See FIXME in
         // adjustLinePositionForPagination() for more details.
         LayoutRect overflow = line->logicalVisualOverflowRect(line->lineTop(), line->lineBottom());
         lineTop = min(line->lineTopWithLeading(), overflow.y());
     }
     return lineBottom - lineTop;
 }

 void RenderBlockFlow::adjustLinePositionForPagination(RootInlineBox* lineBox, LayoutUnit& delta, RenderFlowThread* flowThread)
 {
     // FIXME: For now we paginate using line overflow. This ensures that lines don't overlap at all when we
     // put a strut between them for pagination purposes. However, this really isn't the desired rendering, since
     // the line on the top of the next page will appear too far down relative to the same kind of line at the top
     // of the first column.
     //
     // The rendering we would like to see is one where the lineTopWithLeading is at the top of the column, and any line overflow
     // simply spills out above the top of the column. This effect would match what happens at the top of the first column.
     // We can't achieve this rendering, however, until we stop columns from clipping to the column bounds (thus allowing
     // for overflow to occur), and then cache visible overflow for each column rect.
     //
     // Furthermore, the paint we have to do when a column has overflow has to be special. We need to exclude
     // content that paints in a previous column (and content that paints in the following column).
     //
     // For now we'll at least honor the lineTopWithLeading when paginating if it is above the logical top overflow. This will
     // at least make positive leading work in typical cases.
     //
     // FIXME: Another problem with simply moving lines is that the available line width may change (because of floats).
     // Technically if the location we move the line to has a different line width than our old position, then we need to dirty the
     // line and all following lines.
     LayoutRect logicalVisualOverflow = lineBox->logicalVisualOverflowRect(lineBox->lineTop(), lineBox->lineBottom());
     LayoutUnit logicalOffset = min(lineBox->lineTopWithLeading(), logicalVisualOverflow.y());
     LayoutUnit logicalBottom = max(lineBox->lineBottomWithLeading(), logicalVisualOverflow.maxY());
     LayoutUnit lineHeight = logicalBottom - logicalOffset;
     updateMinimumPageHeight(logicalOffset, calculateMinimumPageHeight(&style(), lineBox, logicalOffset, logicalBottom));
     logicalOffset += delta;
     lineBox->setPaginationStrut(0);
     lineBox->setIsFirstAfterPageBreak(false);
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
     bool hasUniformPageLogicalHeight = !flowThread || flowThread->regionsHaveUniformLogicalHeight();
     // If lineHeight is greater than pageLogicalHeight, but logicalVisualOverflow.height() still fits, we are
     // still going to add a strut, so that the visible overflow fits on a single page.
     if (!pageLogicalHeight || (hasUniformPageLogicalHeight && logicalVisualOverflow.height() > pageLogicalHeight)
         || !hasNextPage(logicalOffset))
         // FIXME: In case the line aligns with the top of the page (or it's slightly shifted downwards) it will not be marked as the first line in the page.
         // From here, the fix is not straightforward because it's not easy to always determine when the current line is the first in the page.
         return;
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);

     int lineIndex = lineCount(lineBox);
     if (remainingLogicalHeight < lineHeight || (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex)) {
         if (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex) {
             clearShouldBreakAtLineToAvoidWidow();
             setDidBreakAtLineToAvoidWidow();
         }
         // If we have a non-uniform page height, then we have to shift further possibly.
         if (!hasUniformPageLogicalHeight && !pushToNextPageWithMinimumLogicalHeight(remainingLogicalHeight, logicalOffset, lineHeight))
             return;
         if (lineHeight > pageLogicalHeight) {
             // Split the top margin in order to avoid splitting the visible part of the line.
             remainingLogicalHeight -= min(lineHeight - pageLogicalHeight, max<LayoutUnit>(0, logicalVisualOverflow.y() - lineBox->lineTopWithLeading()));
         }
         LayoutUnit totalLogicalHeight = lineHeight + max<LayoutUnit>(0, logicalOffset);
         LayoutUnit pageLogicalHeightAtNewOffset = hasUniformPageLogicalHeight ? pageLogicalHeight : pageLogicalHeightForOffset(logicalOffset + remainingLogicalHeight);
         setPageBreak(logicalOffset, lineHeight - remainingLogicalHeight);
         if (((lineBox == firstRootBox() && totalLogicalHeight < pageLogicalHeightAtNewOffset) || (!style().hasAutoOrphans() && style().orphans() >= lineIndex))
             && !isOutOfFlowPositioned() && !isTableCell())
             setPaginationStrut(remainingLogicalHeight + max<LayoutUnit>(0, logicalOffset));
         else {
             delta += remainingLogicalHeight;
             lineBox->setPaginationStrut(remainingLogicalHeight);
             lineBox->setIsFirstAfterPageBreak(true);
         }
     } else if (remainingLogicalHeight == pageLogicalHeight && lineBox != firstRootBox())
         lineBox->setIsFirstAfterPageBreak(true);
 }

 void RenderBlockFlow::setBreakAtLineToAvoidWidow(int lineToBreak)
 {
     ASSERT(lineToBreak >= 0);
     if (!m_rareData)
         m_rareData = adoptPtr(new RenderBlockFlowRareData(*this));

     ASSERT(!m_rareData->m_didBreakAtLineToAvoidWidow);
     m_rareData->m_lineBreakToAvoidWidow = lineToBreak;
 }

 void RenderBlockFlow::setDidBreakAtLineToAvoidWidow()
 {
     ASSERT(!shouldBreakAtLineToAvoidWidow());
     if (!m_rareData)
         return;

     m_rareData->m_didBreakAtLineToAvoidWidow = true;
 }

 void RenderBlockFlow::clearDidBreakAtLineToAvoidWidow()
 {
     if (!m_rareData)
         return;

     m_rareData->m_didBreakAtLineToAvoidWidow = false;
 }

 void RenderBlockFlow::clearShouldBreakAtLineToAvoidWidow() const
 {
     ASSERT(shouldBreakAtLineToAvoidWidow());
     if (!m_rareData)
         return;

     m_rareData->m_lineBreakToAvoidWidow = -1;
 }

 bool RenderBlockFlow::relayoutToAvoidWidows(LayoutStateMaintainer& statePusher)
 {
     if (!shouldBreakAtLineToAvoidWidow())
         return false;

     statePusher.pop();
     setEverHadLayout(true);
     layoutBlock(false);
     return true;
 }

 bool RenderBlockFlow::hasNextPage(LayoutUnit logicalOffset, PageBoundaryRule pageBoundaryRule) const
 {
     ASSERT(view().layoutState() && view().layoutState()->isPaginated());

     RenderFlowThread* flowThread = flowThreadContainingBlock();
     if (!flowThread)
         return true; // Printing and multi-column both make new pages to accommodate content.

     // See if we're in the last region.
     LayoutUnit pageOffset = offsetFromLogicalTopOfFirstPage() + logicalOffset;
     RenderRegion* region = flowThread->regionAtBlockOffset(this, pageOffset, this);
     if (!region)
         return false;
     if (region->isLastRegion())
         return region->isRenderRegionSet() || region->style().regionFragment() == BreakRegionFragment
             || (pageBoundaryRule == IncludePageBoundary && pageOffset == region->logicalTopForFlowThreadContent());
     return true;
 }

 LayoutUnit RenderBlockFlow::adjustForUnsplittableChild(RenderBox& child, LayoutUnit logicalOffset, bool includeMargins)
 {
     bool checkColumnBreaks = view().layoutState()->isPaginatingColumns();
     bool checkPageBreaks = !checkColumnBreaks && view().layoutState()->m_pageLogicalHeight;
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     bool checkRegionBreaks = flowThread && flowThread->isRenderNamedFlowThread();
     bool isUnsplittable = child.isUnsplittableForPagination() || (checkColumnBreaks && child.style().columnBreakInside() == PBAVOID)
         || (checkPageBreaks && child.style().pageBreakInside() == PBAVOID)
         || (checkRegionBreaks && child.style().regionBreakInside() == PBAVOID);
     if (!isUnsplittable)
         return logicalOffset;
     LayoutUnit childLogicalHeight = logicalHeightForChild(child) + (includeMargins ? marginBeforeForChild(child) + marginAfterForChild(child) : LayoutUnit());
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
     bool hasUniformPageLogicalHeight = !flowThread || flowThread->regionsHaveUniformLogicalHeight();
     updateMinimumPageHeight(logicalOffset, childLogicalHeight);
     if (!pageLogicalHeight || (hasUniformPageLogicalHeight && childLogicalHeight > pageLogicalHeight)
         || !hasNextPage(logicalOffset))
         return logicalOffset;
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);
     if (remainingLogicalHeight < childLogicalHeight) {
         if (!hasUniformPageLogicalHeight && !pushToNextPageWithMinimumLogicalHeight(remainingLogicalHeight, logicalOffset, childLogicalHeight))
             return logicalOffset;
         return logicalOffset + remainingLogicalHeight;
     }
     return logicalOffset;
 }

 bool RenderBlockFlow::pushToNextPageWithMinimumLogicalHeight(LayoutUnit& adjustment, LayoutUnit logicalOffset, LayoutUnit minimumLogicalHeight) const
 {
     bool checkRegion = false;
     for (LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset + adjustment); pageLogicalHeight;
         pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset + adjustment)) {
         if (minimumLogicalHeight <= pageLogicalHeight)
             return true;
         if (!hasNextPage(logicalOffset + adjustment))
             return false;
         adjustment += pageLogicalHeight;
         checkRegion = true;
     }
     return !checkRegion;
 }

 void RenderBlockFlow::setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage)
 {
     if (RenderFlowThread* flowThread = flowThreadContainingBlock())
         flowThread->setPageBreak(this, offsetFromLogicalTopOfFirstPage() + offset, spaceShortage);
 }

 void RenderBlockFlow::updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight)
 {
     if (RenderFlowThread* flowThread = flowThreadContainingBlock())
         flowThread->updateMinimumPageHeight(this, offsetFromLogicalTopOfFirstPage() + offset, minHeight);
     else if (ColumnInfo* colInfo = view().layoutState()->m_columnInfo)
         colInfo->updateMinimumColumnHeight(minHeight);
 }

 LayoutUnit RenderBlockFlow::nextPageLogicalTop(LayoutUnit logicalOffset, PageBoundaryRule pageBoundaryRule) const
 {
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
     if (!pageLogicalHeight)
         return logicalOffset;

     // The logicalOffset is in our coordinate space.  We can add in our pushed offset.
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset);
     if (pageBoundaryRule == ExcludePageBoundary)
         return logicalOffset + (remainingLogicalHeight ? remainingLogicalHeight : pageLogicalHeight);
     return logicalOffset + remainingLogicalHeight;
 }

 LayoutUnit RenderBlockFlow::pageLogicalTopForOffset(LayoutUnit offset) const
 {
     LayoutUnit firstPageLogicalTop = isHorizontalWritingMode() ? view().layoutState()->m_pageOffset.height() : view().layoutState()->m_pageOffset.width();
     LayoutUnit blockLogicalTop = isHorizontalWritingMode() ? view().layoutState()->m_layoutOffset.height() : view().layoutState()->m_layoutOffset.width();

     LayoutUnit cumulativeOffset = offset + blockLogicalTop;
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     if (!flowThread) {
         LayoutUnit pageLogicalHeight = view().layoutState()->pageLogicalHeight();
         if (!pageLogicalHeight)
             return 0;
         return cumulativeOffset - roundToInt(cumulativeOffset - firstPageLogicalTop) % roundToInt(pageLogicalHeight);
     }
     return flowThread->pageLogicalTopForOffset(cumulativeOffset);
 }

 LayoutUnit RenderBlockFlow::pageLogicalHeightForOffset(LayoutUnit offset) const
 {
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     if (!flowThread)
         return view().layoutState()->m_pageLogicalHeight;
     return flowThread->pageLogicalHeightForOffset(offset + offsetFromLogicalTopOfFirstPage());
 }

 LayoutUnit RenderBlockFlow::pageRemainingLogicalHeightForOffset(LayoutUnit offset, PageBoundaryRule pageBoundaryRule) const
 {
     offset += offsetFromLogicalTopOfFirstPage();

     RenderFlowThread* flowThread = flowThreadContainingBlock();
     if (!flowThread) {
         LayoutUnit pageLogicalHeight = view().layoutState()->m_pageLogicalHeight;
         LayoutUnit remainingHeight = pageLogicalHeight - intMod(offset, pageLogicalHeight);
         if (pageBoundaryRule == IncludePageBoundary) {
             // If includeBoundaryPoint is true the line exactly on the top edge of a
             // column will act as being part of the previous column.
             remainingHeight = intMod(remainingHeight, pageLogicalHeight);
         }
         return remainingHeight;
     }

     return flowThread->pageRemainingLogicalHeightForOffset(offset, pageBoundaryRule);
 }


 void RenderBlockFlow::layoutLineGridBox()
 {
     if (style().lineGrid() == RenderStyle::initialLineGrid()) {
         setLineGridBox(0);
         return;
     }

     setLineGridBox(0);

     RootInlineBox* lineGridBox = new RootInlineBox(*this);
     lineGridBox->setHasTextChildren(); // Needed to make the line ascent/descent actually be honored in quirks mode.
     lineGridBox->setConstructed();
     GlyphOverflowAndFallbackFontsMap textBoxDataMap;
     VerticalPositionCache verticalPositionCache;
     lineGridBox->alignBoxesInBlockDirection(logicalHeight(), textBoxDataMap, verticalPositionCache);

     setLineGridBox(lineGridBox);

     // FIXME: If any of the characteristics of the box change compared to the old one, then we need to do a deep dirtying
     // (similar to what happens when the page height changes). Ideally, though, we only do this if someone is actually snapping
     // to this grid.
 }

 bool RenderBlockFlow::containsFloat(RenderBox& renderer) const
 {
     return m_floatingObjects && m_floatingObjects->set().contains<RenderBox&, FloatingObjectHashTranslator>(renderer);
 }

 void RenderBlockFlow::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
 {
     RenderBlock::styleDidChange(diff, oldStyle);

     // After our style changed, if we lose our ability to propagate floats into next sibling
     // blocks, then we need to find the top most parent containing that overhanging float and
     // then mark its descendants with floats for layout and clear all floats from its next
     // sibling blocks that exist in our floating objects list. See bug 56299 and 62875.
     bool canPropagateFloatIntoSibling = !isFloatingOrOutOfFlowPositioned() && !avoidsFloats();
     if (diff == StyleDifferenceLayout && s_canPropagateFloatIntoSibling && !canPropagateFloatIntoSibling && hasOverhangingFloats()) {
         RenderBlockFlow* parentBlock = this;
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         auto end = floatingObjectSet.end();

         for (auto curr = parent(); curr && !curr->isRenderView(); curr = curr->parent()) {
             if (curr->isRenderBlockFlow()) {
                 RenderBlockFlow* currBlock = toRenderBlockFlow(curr);

                 if (currBlock->hasOverhangingFloats()) {
                     for (auto it = floatingObjectSet.begin(); it != end; ++it) {
                         RenderBox& renderer = (*it)->renderer();
                         if (currBlock->hasOverhangingFloat(renderer)) {
                             parentBlock = currBlock;
                             break;
                         }
                     }
                 }
             }
         }

         parentBlock->markAllDescendantsWithFloatsForLayout();
         parentBlock->markSiblingsWithFloatsForLayout();
     }

     if (auto fragment = renderNamedFlowFragment())
         fragment->setStyle(RenderNamedFlowFragment::createStyle(style()));

     if (diff >= StyleDifferenceRepaint)
         invalidateLineLayoutPath();
 }

 void RenderBlockFlow::styleWillChange(StyleDifference diff, const RenderStyle& newStyle)
 {
     const RenderStyle* oldStyle = hasInitializedStyle() ? &style() : nullptr;
     s_canPropagateFloatIntoSibling = oldStyle ? !isFloatingOrOutOfFlowPositioned() && !avoidsFloats() : false;

     if (oldStyle && parent() && diff == StyleDifferenceLayout && oldStyle->position() != newStyle.position()) {
         if (containsFloats() && !isFloating() && !isOutOfFlowPositioned() && newStyle.hasOutOfFlowPosition())
             markAllDescendantsWithFloatsForLayout();
     }

     RenderBlock::styleWillChange(diff, newStyle);
 }

 void RenderBlockFlow::deleteLines()
 {
     if (containsFloats())
         m_floatingObjects->clearLineBoxTreePointers();

     if (m_simpleLineLayout) {
         ASSERT(!m_lineBoxes.firstLineBox());
         m_simpleLineLayout = nullptr;
     } else
         m_lineBoxes.deleteLineBoxTree();

     RenderBlock::deleteLines();
 }

 void RenderBlockFlow::moveAllChildrenIncludingFloatsTo(RenderBlock* toBlock, bool fullRemoveInsert)
 {
     RenderBlockFlow* toBlockFlow = toRenderBlockFlow(toBlock);
     moveAllChildrenTo(toBlockFlow, fullRemoveInsert);

     // When a portion of the render tree is being detached, anonymous blocks
     // will be combined as their children are deleted. In this process, the
     // anonymous block later in the tree is merged into the one preceeding it.
     // It can happen that the later block (this) contains floats that the
     // previous block (toBlockFlow) did not contain, and thus are not in the
     // floating objects list for toBlockFlow. This can result in toBlockFlow
     // containing floats that are not in it's floating objects list, but are in
     // the floating objects lists of siblings and parents. This can cause
     // problems when the float itself is deleted, since the deletion code
     // assumes that if a float is not in it's containing block's floating
     // objects list, it isn't in any floating objects list. In order to
     // preserve this condition (removing it has serious performance
     // implications), we need to copy the floating objects from the old block
     // (this) to the new block (toBlockFlow). The float's metrics will likely
     // all be wrong, but since toBlockFlow is already marked for layout, this
     // will get fixed before anything gets displayed.
     // See bug https://bugs.webkit.org/show_bug.cgi?id=115566
     if (m_floatingObjects) {
         if (!toBlockFlow->m_floatingObjects)
             toBlockFlow->createFloatingObjects();

         const FloatingObjectSet& fromFloatingObjectSet = m_floatingObjects->set();
         auto end = fromFloatingObjectSet.end();

         for (auto it = fromFloatingObjectSet.begin(); it != end; ++it) {
             FloatingObject* floatingObject = it->get();

             // Don't insert the object again if it's already in the list
             if (toBlockFlow->containsFloat(floatingObject->renderer()))
                 continue;

             toBlockFlow->m_floatingObjects->add(floatingObject->unsafeClone());
         }
     }
 }

 void RenderBlockFlow::addOverflowFromFloats()
 {
     if (!m_floatingObjects)
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto end = floatingObjectSet.end();
     for (auto it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* r = it->get();
         if (r->isDescendant())
             addOverflowFromChild(&r->renderer(), IntSize(xPositionForFloatIncludingMargin(r), yPositionForFloatIncludingMargin(r)));
     }
 }

 void RenderBlockFlow::computeOverflow(LayoutUnit oldClientAfterEdge, bool recomputeFloats)
 {
     RenderBlock::computeOverflow(oldClientAfterEdge, recomputeFloats);

     if (!hasColumns() && (recomputeFloats || isRoot() || expandsToEncloseOverhangingFloats() || hasSelfPaintingLayer()))
         addOverflowFromFloats();
 }

 void RenderBlockFlow::repaintOverhangingFloats(bool paintAllDescendants)
 {
     // Repaint any overhanging floats (if we know we're the one to paint them).
     // Otherwise, bail out.
     if (!hasOverhangingFloats())
         return;

     // FIXME: Avoid disabling LayoutState. At the very least, don't disable it for floats originating
     // in this block. Better yet would be to push extra state for the containers of other floats.
     LayoutStateDisabler layoutStateDisabler(&view());
     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto end = floatingObjectSet.end();
     for (auto it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         // Only repaint the object if it is overhanging, is not in its own layer, and
         // is our responsibility to paint (m_shouldPaint is set). When paintAllDescendants is true, the latter
         // condition is replaced with being a descendant of us.
         if (logicalBottomForFloat(floatingObject) > logicalHeight()
             && !floatingObject->renderer().hasSelfPaintingLayer()
             && (floatingObject->shouldPaint() || (paintAllDescendants && floatingObject->renderer().isDescendantOf(this)))) {
             floatingObject->renderer().repaint();
             floatingObject->renderer().repaintOverhangingFloats(false);
         }
     }
 }

 void RenderBlockFlow::paintFloats(PaintInfo& paintInfo, const LayoutPoint& paintOffset, bool preservePhase)
 {
     if (!m_floatingObjects)
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto end = floatingObjectSet.end();
     for (auto it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* r = it->get();
         // Only paint the object if our m_shouldPaint flag is set.
         if (r->shouldPaint() && !r->renderer().hasSelfPaintingLayer()) {
             PaintInfo currentPaintInfo(paintInfo);
             currentPaintInfo.phase = preservePhase ? paintInfo.phase : PaintPhaseBlockBackground;
             // FIXME: LayoutPoint version of xPositionForFloatIncludingMargin would make this much cleaner.
             LayoutPoint childPoint = flipFloatForWritingModeForChild(r, LayoutPoint(paintOffset.x() + xPositionForFloatIncludingMargin(r) - r->renderer().x(), paintOffset.y() + yPositionForFloatIncludingMargin(r) - r->renderer().y()));
             r->renderer().paint(currentPaintInfo, childPoint);
             if (!preservePhase) {
                 currentPaintInfo.phase = PaintPhaseChildBlockBackgrounds;
                 r->renderer().paint(currentPaintInfo, childPoint);
                 currentPaintInfo.phase = PaintPhaseFloat;
                 r->renderer().paint(currentPaintInfo, childPoint);
                 currentPaintInfo.phase = PaintPhaseForeground;
                 r->renderer().paint(currentPaintInfo, childPoint);
                 currentPaintInfo.phase = PaintPhaseOutline;
                 r->renderer().paint(currentPaintInfo, childPoint);
             }
         }
     }
 }

 void RenderBlockFlow::clipOutFloatingObjects(RenderBlock& rootBlock, const PaintInfo* paintInfo, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock)
 {
     if (m_floatingObjects) {
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         auto end = floatingObjectSet.end();
         for (auto it = floatingObjectSet.begin(); it != end; ++it) {
             FloatingObject* floatingObject = it->get();
             LayoutRect floatBox(offsetFromRootBlock.width() + xPositionForFloatIncludingMargin(floatingObject),
                 offsetFromRootBlock.height() + yPositionForFloatIncludingMargin(floatingObject),
                 floatingObject->renderer().width(), floatingObject->renderer().height());
             rootBlock.flipForWritingMode(floatBox);
             floatBox.move(rootBlockPhysicalPosition.x(), rootBlockPhysicalPosition.y());
             paintInfo->context->clipOut(pixelSnappedIntRect(floatBox));
         }
     }
 }

 void RenderBlockFlow::createFloatingObjects()
 {
     m_floatingObjects = adoptPtr(new FloatingObjects(this, isHorizontalWritingMode()));
 }

 void RenderBlockFlow::removeFloatingObjects()
 {
     if (!m_floatingObjects)
         return;

     m_floatingObjects->clear();
 }

 FloatingObject* RenderBlockFlow::insertFloatingObject(RenderBox& floatBox)
 {
     ASSERT(floatBox.isFloating());

     // Create the list of special objects if we don't aleady have one
     if (!m_floatingObjects)
         createFloatingObjects();
     else {
         // Don't insert the floatingObject again if it's already in the list
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         auto it = floatingObjectSet.find<RenderBox&, FloatingObjectHashTranslator>(floatBox);
         if (it != floatingObjectSet.end())
             return it->get();
     }

     // Create the special floatingObject entry & append it to the list

     std::unique_ptr<FloatingObject> floatingObject = FloatingObject::create(floatBox);

     // Our location is irrelevant if we're unsplittable or no pagination is in effect.
     // Just go ahead and lay out the float.
     bool isChildRenderBlock = floatBox.isRenderBlock();
     if (isChildRenderBlock && !floatBox.needsLayout() && view().layoutState()->pageLogicalHeightChanged())
         floatBox.setChildNeedsLayout(MarkOnlyThis);

     bool needsBlockDirectionLocationSetBeforeLayout = isChildRenderBlock && view().layoutState()->needsBlockDirectionLocationSetBeforeLayout();
     if (!needsBlockDirectionLocationSetBeforeLayout || isWritingModeRoot()) // We are unsplittable if we're a block flow root.
         floatBox.layoutIfNeeded();
     else {
         floatBox.updateLogicalWidth();
         floatBox.computeAndSetBlockDirectionMargins(this);
     }

     setLogicalWidthForFloat(floatingObject.get(), logicalWidthForChild(floatBox) + marginStartForChild(floatBox) + marginEndForChild(floatBox));

 #if ENABLE(CSS_SHAPES)
     if (ShapeOutsideInfo* shapeOutside = floatBox.shapeOutsideInfo())
         shapeOutside->setShapeSize(logicalWidthForChild(floatBox), logicalHeightForChild(floatBox));
 #endif

     return m_floatingObjects->add(std::move(floatingObject));
 }

 void RenderBlockFlow::removeFloatingObject(RenderBox& floatBox)
 {
     if (m_floatingObjects) {
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         auto it = floatingObjectSet.find<RenderBox&, FloatingObjectHashTranslator>(floatBox);
         if (it != floatingObjectSet.end()) {
             FloatingObject* floatingObject = it->get();
             if (childrenInline()) {
                 LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
                 LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);

                 // Fix for https://bugs.webkit.org/show_bug.cgi?id=54995.
                 if (logicalBottom < 0 || logicalBottom < logicalTop || logicalTop == LayoutUnit::max())
                     logicalBottom = LayoutUnit::max();
                 else {
                     // Special-case zero- and less-than-zero-height floats: those don't touch
                     // the line that they're on, but it still needs to be dirtied. This is
                     // accomplished by pretending they have a height of 1.
                     logicalBottom = max(logicalBottom, logicalTop + 1);
                 }
                 if (floatingObject->originatingLine()) {
                     if (!selfNeedsLayout()) {
                         ASSERT(&floatingObject->originatingLine()->renderer() == this);
                         floatingObject->originatingLine()->markDirty();
                     }
 #if !ASSERT_DISABLED
                     floatingObject->setOriginatingLine(0);
 #endif
                 }
                 markLinesDirtyInBlockRange(0, logicalBottom);
             }
             m_floatingObjects->remove(floatingObject);
         }
     }
 }

 void RenderBlockFlow::removeFloatingObjectsBelow(FloatingObject* lastFloat, int logicalOffset)
 {
     if (!containsFloats())
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObject* curr = floatingObjectSet.last().get();
     while (curr != lastFloat && (!curr->isPlaced() || logicalTopForFloat(curr) >= logicalOffset)) {
         m_floatingObjects->remove(curr);
         if (floatingObjectSet.isEmpty())
             break;
         curr = floatingObjectSet.last().get();
     }
 }

 LayoutPoint RenderBlockFlow::computeLogicalLocationForFloat(const FloatingObject* floatingObject, LayoutUnit logicalTopOffset) const
 {
     RenderBox& childBox = floatingObject->renderer();
     LayoutUnit logicalLeftOffset = logicalLeftOffsetForContent(logicalTopOffset); // Constant part of left offset.
     LayoutUnit logicalRightOffset; // Constant part of right offset.
 #if ENABLE(CSS_SHAPES)
     // FIXME Bug 102948: This only works for shape outside directly set on this block.
     ShapeInsideInfo* shapeInsideInfo = this->layoutShapeInsideInfo();
     // FIXME: Implement behavior for right floats.
     if (shapeInsideInfo) {
         LayoutSize floatLogicalSize = logicalSizeForFloat(floatingObject);
         // floatingObject's logicalSize doesn't contain the actual height at this point, so we need to calculate it
         floatLogicalSize.setHeight(logicalHeightForChild(childBox) + marginBeforeForChild(childBox) + marginAfterForChild(childBox));

         // FIXME: If the float doesn't fit in the shape we should push it under the content box
         logicalTopOffset = shapeInsideInfo->computeFirstFitPositionForFloat(floatLogicalSize);
         if (logicalHeight() > logicalTopOffset)
             logicalTopOffset = logicalHeight();

         SegmentList segments = shapeInsideInfo->computeSegmentsForLine(logicalTopOffset, floatLogicalSize.height());
         // FIXME Bug 102949: Add support for shapes with multiple segments.
         if (segments.size() == 1) {
             // The segment offsets are relative to the content box.
             logicalRightOffset = logicalLeftOffset + segments[0].logicalRight;
             logicalLeftOffset += segments[0].logicalLeft;
         }
     } else
 #endif
         logicalRightOffset = logicalRightOffsetForContent(logicalTopOffset);

     LayoutUnit floatLogicalWidth = min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset); // The width we look for.

     LayoutUnit floatLogicalLeft;

     bool insideFlowThread = flowThreadContainingBlock();

     if (childBox.style().floating() == LeftFloat) {
         LayoutUnit heightRemainingLeft = 1;
         LayoutUnit heightRemainingRight = 1;
         floatLogicalLeft = logicalLeftOffsetForLineIgnoringShapeOutside(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
         while (logicalRightOffsetForLineIgnoringShapeOutside(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight) - floatLogicalLeft < floatLogicalWidth) {
             logicalTopOffset += min(heightRemainingLeft, heightRemainingRight);
             floatLogicalLeft = logicalLeftOffsetForLineIgnoringShapeOutside(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
             if (insideFlowThread) {
                 // Have to re-evaluate all of our offsets, since they may have changed.
                 logicalRightOffset = logicalRightOffsetForContent(logicalTopOffset); // Constant part of right offset.
                 logicalLeftOffset = logicalLeftOffsetForContent(logicalTopOffset); // Constant part of left offset.
                 floatLogicalWidth = min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
             }
         }
         floatLogicalLeft = max(logicalLeftOffset - borderAndPaddingLogicalLeft(), floatLogicalLeft);
     } else {
         LayoutUnit heightRemainingLeft = 1;
         LayoutUnit heightRemainingRight = 1;
         floatLogicalLeft = logicalRightOffsetForLineIgnoringShapeOutside(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
         while (floatLogicalLeft - logicalLeftOffsetForLineIgnoringShapeOutside(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft) < floatLogicalWidth) {
             logicalTopOffset += min(heightRemainingLeft, heightRemainingRight);
             floatLogicalLeft = logicalRightOffsetForLineIgnoringShapeOutside(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
             if (insideFlowThread) {
                 // Have to re-evaluate all of our offsets, since they may have changed.
                 logicalRightOffset = logicalRightOffsetForContent(logicalTopOffset); // Constant part of right offset.
                 logicalLeftOffset = logicalLeftOffsetForContent(logicalTopOffset); // Constant part of left offset.
                 floatLogicalWidth = min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
             }
         }
         // Use the original width of the float here, since the local variable
         // |floatLogicalWidth| was capped to the available line width. See
         // fast/block/float/clamped-right-float.html.
         floatLogicalLeft -= logicalWidthForFloat(floatingObject);
     }

     return LayoutPoint(floatLogicalLeft, logicalTopOffset);
 }

 bool RenderBlockFlow::positionNewFloats()
 {
     if (!m_floatingObjects)
         return false;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     if (floatingObjectSet.isEmpty())
         return false;

     // If all floats have already been positioned, then we have no work to do.
     if (floatingObjectSet.last()->isPlaced())
         return false;

     // Move backwards through our floating object list until we find a float that has
     // already been positioned. Then we'll be able to move forward, positioning all of
     // the new floats that need it.
     auto it = floatingObjectSet.end();
     --it; // Go to last item.
     auto begin = floatingObjectSet.begin();
     FloatingObject* lastPlacedFloatingObject = 0;
     while (it != begin) {
         --it;
         if ((*it)->isPlaced()) {
             lastPlacedFloatingObject = it->get();
             ++it;
             break;
         }
     }

     LayoutUnit logicalTop = logicalHeight();

     // The float cannot start above the top position of the last positioned float.
     if (lastPlacedFloatingObject)
         logicalTop = max(logicalTopForFloat(lastPlacedFloatingObject), logicalTop);

     auto end = floatingObjectSet.end();
     // Now walk through the set of unpositioned floats and place them.
     for (; it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         // The containing block is responsible for positioning floats, so if we have floats in our
         // list that come from somewhere else, do not attempt to position them.
         if (floatingObject->renderer().containingBlock() != this)
             continue;

         RenderBox& childBox = floatingObject->renderer();

         LayoutUnit childLogicalLeftMargin = style().isLeftToRightDirection() ? marginStartForChild(childBox) : marginEndForChild(childBox);

         LayoutRect oldRect = childBox.frameRect();

         if (childBox.style().clear() & CLEFT)
             logicalTop = max(lowestFloatLogicalBottom(FloatingObject::FloatLeft), logicalTop);
         if (childBox.style().clear() & CRIGHT)
             logicalTop = max(lowestFloatLogicalBottom(FloatingObject::FloatRight), logicalTop);

         LayoutPoint floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, logicalTop);

         setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

         setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
         setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));

         estimateRegionRangeForBoxChild(childBox);

         LayoutState* layoutState = view().layoutState();
         bool isPaginated = layoutState->isPaginated();
         if (isPaginated && !childBox.needsLayout())
             childBox.markForPaginationRelayoutIfNeeded();

         childBox.layoutIfNeeded();

         if (isPaginated) {
             // If we are unsplittable and don't fit, then we need to move down.
             // We include our margins as part of the unsplittable area.
             LayoutUnit newLogicalTop = adjustForUnsplittableChild(childBox, floatLogicalLocation.y(), true);

             // See if we have a pagination strut that is making us move down further.
             // Note that an unsplittable child can't also have a pagination strut, so this is
             // exclusive with the case above.
             RenderBlock* childBlock = childBox.isRenderBlock() ? toRenderBlock(&childBox) : nullptr;
             if (childBlock && childBlock->paginationStrut()) {
                 newLogicalTop += childBlock->paginationStrut();
                 childBlock->setPaginationStrut(0);
             }

             if (newLogicalTop != floatLogicalLocation.y()) {
                 floatingObject->setPaginationStrut(newLogicalTop - floatLogicalLocation.y());

                 floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, newLogicalTop);
                 setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

                 setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
                 setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));

                 if (childBlock)
                     childBlock->setChildNeedsLayout(MarkOnlyThis);
                 childBox.layoutIfNeeded();
             }

             if (updateRegionRangeForBoxChild(childBox)) {
                 childBox.setNeedsLayout(MarkOnlyThis);
                 childBox.layoutIfNeeded();
             }
         }

         setLogicalTopForFloat(floatingObject, floatLogicalLocation.y());

         setLogicalHeightForFloat(floatingObject, logicalHeightForChild(childBox) + marginBeforeForChild(childBox) + marginAfterForChild(childBox));

         m_floatingObjects->addPlacedObject(floatingObject);

         // If the child moved, we have to repaint it.
         if (childBox.checkForRepaintDuringLayout())
             childBox.repaintDuringLayoutIfMoved(oldRect);
     }
     return true;
 }

 void RenderBlockFlow::newLine(EClear clear)
 {
     positionNewFloats();
     // set y position
     LayoutUnit newY = 0;
     switch (clear) {
     case CLEFT:
         newY = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
         break;
     case CRIGHT:
         newY = lowestFloatLogicalBottom(FloatingObject::FloatRight);
         break;
     case CBOTH:
         newY = lowestFloatLogicalBottom();
     default:
         break;
     }
     if (height() < newY)
         setLogicalHeight(newY);
 }

 LayoutUnit RenderBlockFlow::logicalLeftFloatOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, LayoutUnit* heightRemaining, LayoutUnit logicalHeight, ShapeOutsideFloatOffsetMode offsetMode) const
 {
     if (m_floatingObjects && m_floatingObjects->hasLeftObjects())
         return m_floatingObjects->logicalLeftOffset(fixedOffset, logicalTop, logicalHeight, offsetMode, heightRemaining);

     return fixedOffset;
 }

 LayoutUnit RenderBlockFlow::logicalRightFloatOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, LayoutUnit* heightRemaining, LayoutUnit logicalHeight, ShapeOutsideFloatOffsetMode offsetMode) const
 {
     if (m_floatingObjects && m_floatingObjects->hasRightObjects())
         return m_floatingObjects->logicalRightOffset(fixedOffset, logicalTop, logicalHeight, offsetMode, heightRemaining);

     return fixedOffset;
 }

 LayoutUnit RenderBlockFlow::nextFloatLogicalBottomBelow(LayoutUnit logicalHeight, ShapeOutsideFloatOffsetMode offsetMode) const
 {
     if (!m_floatingObjects)
         return logicalHeight;

     LayoutUnit bottom = LayoutUnit::max();
     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto end = floatingObjectSet.end();
     for (auto it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         LayoutUnit floatBottom = logicalBottomForFloat(floatingObject);
 #if ENABLE(CSS_SHAPES)
         ShapeOutsideInfo* shapeOutside = floatingObject->renderer().shapeOutsideInfo();
         if (offsetMode == ShapeOutsideFloatShapeOffset && shapeOutside) {
             LayoutUnit shapeBottom = logicalTopForFloat(floatingObject) + marginBeforeForChild(floatingObject->renderer()) + shapeOutside->shapeLogicalBottom();
             // Use the shapeBottom unless it extends outside of the margin box, in which case it is clipped.
             if (shapeBottom < floatBottom)
                 floatBottom = shapeBottom;
         }
 #endif
         if (floatBottom > logicalHeight)
             bottom = min(floatBottom, bottom);
     }

     return bottom == LayoutUnit::max() ? LayoutUnit() : bottom;
 }

 LayoutUnit RenderBlockFlow::lowestFloatLogicalBottom(FloatingObject::Type floatType) const
 {
     if (!m_floatingObjects)
         return 0;
     LayoutUnit lowestFloatBottom = 0;
     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto end = floatingObjectSet.end();
     for (auto it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         if (floatingObject->isPlaced() && floatingObject->type() & floatType)
             lowestFloatBottom = max(lowestFloatBottom, logicalBottomForFloat(floatingObject));
     }
     return lowestFloatBottom;
 }

 LayoutUnit RenderBlockFlow::addOverhangingFloats(RenderBlockFlow& child, bool makeChildPaintOtherFloats)
 {
     // Prevent floats from being added to the canvas by the root element, e.g., <html>.
     if (child.hasOverflowClip() || !child.containsFloats() || child.isRoot() || child.hasColumns() || child.isWritingModeRoot())
         return 0;

     LayoutUnit childLogicalTop = child.logicalTop();
     LayoutUnit childLogicalLeft = child.logicalLeft();
     LayoutUnit lowestFloatLogicalBottom = 0;

     // Floats that will remain the child's responsibility to paint should factor into its
     // overflow.
     auto childEnd = child.m_floatingObjects->set().end();
     for (auto childIt = child.m_floatingObjects->set().begin(); childIt != childEnd; ++childIt) {
         FloatingObject* floatingObject = childIt->get();
         LayoutUnit floatLogicalBottom = min(logicalBottomForFloat(floatingObject), LayoutUnit::max() - childLogicalTop);
         LayoutUnit logicalBottom = childLogicalTop + floatLogicalBottom;
         lowestFloatLogicalBottom = max(lowestFloatLogicalBottom, logicalBottom);

         if (logicalBottom > logicalHeight()) {
             // If the object is not in the list, we add it now.
             if (!containsFloat(floatingObject->renderer())) {
                 LayoutSize offset = isHorizontalWritingMode() ? LayoutSize(-childLogicalLeft, -childLogicalTop) : LayoutSize(-childLogicalTop, -childLogicalLeft);
                 bool shouldPaint = false;

                 // The nearest enclosing layer always paints the float (so that zindex and stacking
                 // behaves properly). We always want to propagate the desire to paint the float as
                 // far out as we can, to the outermost block that overlaps the float, stopping only
                 // if we hit a self-painting layer boundary.
                 if (floatingObject->renderer().enclosingFloatPaintingLayer() == enclosingFloatPaintingLayer()) {
                     floatingObject->setShouldPaint(false);
                     shouldPaint = true;
                 }
                 // We create the floating object list lazily.
                 if (!m_floatingObjects)
                     createFloatingObjects();

                 m_floatingObjects->add(floatingObject->copyToNewContainer(offset, shouldPaint, true));
             }
         } else {
             if (makeChildPaintOtherFloats && !floatingObject->shouldPaint() && !floatingObject->renderer().hasSelfPaintingLayer()
                 && floatingObject->renderer().isDescendantOf(&child) && floatingObject->renderer().enclosingFloatPaintingLayer() == child.enclosingFloatPaintingLayer()) {
                 // The float is not overhanging from this block, so if it is a descendant of the child, the child should
                 // paint it (the other case is that it is intruding into the child), unless it has its own layer or enclosing
                 // layer.
                 // If makeChildPaintOtherFloats is false, it means that the child must already know about all the floats
                 // it should paint.
                 floatingObject->setShouldPaint(true);
             }

             // Since the float doesn't overhang, it didn't get put into our list. We need to go ahead and add its overflow in to the
             // child now.
             if (floatingObject->isDescendant())
                 child.addOverflowFromChild(&floatingObject->renderer(), LayoutSize(xPositionForFloatIncludingMargin(floatingObject), yPositionForFloatIncludingMargin(floatingObject)));
         }
     }
     return lowestFloatLogicalBottom;
 }

 bool RenderBlockFlow::hasOverhangingFloat(RenderBox& renderer)
 {
     if (!m_floatingObjects || hasColumns() || !parent())
         return false;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto it = floatingObjectSet.find<RenderBox&, FloatingObjectHashTranslator>(renderer);
     if (it == floatingObjectSet.end())
         return false;

     return logicalBottomForFloat(it->get()) > logicalHeight();
 }

 void RenderBlockFlow::addIntrudingFloats(RenderBlockFlow* prev, LayoutUnit logicalLeftOffset, LayoutUnit logicalTopOffset)
 {
     ASSERT(!avoidsFloats());

     // If the parent or previous sibling doesn't have any floats to add, don't bother.
     if (!prev->m_floatingObjects)
         return;

     logicalLeftOffset += marginLogicalLeft();

     const FloatingObjectSet& prevSet = prev->m_floatingObjects->set();
     auto prevEnd = prevSet.end();
     for (auto prevIt = prevSet.begin(); prevIt != prevEnd; ++prevIt) {
         FloatingObject* floatingObject = prevIt->get();
         if (logicalBottomForFloat(floatingObject) > logicalTopOffset) {
             if (!m_floatingObjects || !m_floatingObjects->set().contains<FloatingObject&, FloatingObjectHashTranslator>(*floatingObject)) {
                 // We create the floating object list lazily.
                 if (!m_floatingObjects)
                     createFloatingObjects();

                 // Applying the child's margin makes no sense in the case where the child was passed in.
                 // since this margin was added already through the modification of the |logicalLeftOffset| variable
                 // above. |logicalLeftOffset| will equal the margin in this case, so it's already been taken
                 // into account. Only apply this code if prev is the parent, since otherwise the left margin
                 // will get applied twice.
                 LayoutSize offset = isHorizontalWritingMode()
                     ? LayoutSize(logicalLeftOffset - (prev != parent() ? prev->marginLeft() : LayoutUnit()), logicalTopOffset)
                     : LayoutSize(logicalTopOffset, logicalLeftOffset - (prev != parent() ? prev->marginTop() : LayoutUnit()));

                 m_floatingObjects->add(floatingObject->copyToNewContainer(offset));
             }
         }
     }
 }

 void RenderBlockFlow::markAllDescendantsWithFloatsForLayout(RenderBox* floatToRemove, bool inLayout)
 {
     if (!everHadLayout() && !containsFloats())
         return;

     MarkingBehavior markParents = inLayout ? MarkOnlyThis : MarkContainingBlockChain;
     setChildNeedsLayout(markParents);

     if (floatToRemove)
         removeFloatingObject(*floatToRemove);

     // Iterate over our children and mark them as needed.
     if (!childrenInline()) {
         for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
             if ((!floatToRemove && child->isFloatingOrOutOfFlowPositioned()) || !child->isRenderBlock())
                 continue;
             if (!child->isRenderBlockFlow()) {
                 RenderBlock* childBlock = toRenderBlock(child);
                 if (childBlock->shrinkToAvoidFloats() && childBlock->everHadLayout())
                     childBlock->setChildNeedsLayout(markParents);
                 continue;
             }
             RenderBlockFlow* childBlock = toRenderBlockFlow(child);
             if ((floatToRemove ? childBlock->containsFloat(*floatToRemove) : childBlock->containsFloats()) || childBlock->shrinkToAvoidFloats())
                 childBlock->markAllDescendantsWithFloatsForLayout(floatToRemove, inLayout);
         }
     }
 }

 void RenderBlockFlow::markSiblingsWithFloatsForLayout(RenderBox* floatToRemove)
 {
     if (!m_floatingObjects)
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto end = floatingObjectSet.end();

     for (RenderObject* next = nextSibling(); next; next = next->nextSibling()) {
         if (!next->isRenderBlockFlow() || next->isFloatingOrOutOfFlowPositioned() || toRenderBlock(next)->avoidsFloats())
             continue;

         RenderBlockFlow* nextBlock = toRenderBlockFlow(next);
         for (auto it = floatingObjectSet.begin(); it != end; ++it) {
             RenderBox& floatingBox = (*it)->renderer();
             if (floatToRemove && &floatingBox != floatToRemove)
                 continue;
             if (nextBlock->containsFloat(floatingBox))
                 nextBlock->markAllDescendantsWithFloatsForLayout(&floatingBox);
         }
     }
 }

 LayoutPoint RenderBlockFlow::flipFloatForWritingModeForChild(const FloatingObject* child, const LayoutPoint& point) const
 {
     if (!style().isFlippedBlocksWritingMode())
         return point;

     // This is similar to RenderBox::flipForWritingModeForChild. We have to subtract out our left/top offsets twice, since
     // it's going to get added back in. We hide this complication here so that the calling code looks normal for the unflipped
     // case.
     if (isHorizontalWritingMode())
         return LayoutPoint(point.x(), point.y() + height() - child->renderer().height() - 2 * yPositionForFloatIncludingMargin(child));
     return LayoutPoint(point.x() + width() - child->renderer().width() - 2 * xPositionForFloatIncludingMargin(child), point.y());
 }

 LayoutUnit RenderBlockFlow::getClearDelta(RenderBox& child, LayoutUnit logicalTop)
 {
     // There is no need to compute clearance if we have no floats.
     if (!containsFloats())
         return 0;

     // At least one float is present. We need to perform the clearance computation.
     bool clearSet = child.style().clear() != CNONE;
     LayoutUnit logicalBottom = 0;
     switch (child.style().clear()) {
     case CNONE:
         break;
     case CLEFT:
         logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
         break;
     case CRIGHT:
         logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatRight);
         break;
     case CBOTH:
         logicalBottom = lowestFloatLogicalBottom();
         break;
     }

     // We also clear floats if we are too big to sit on the same line as a float (and wish to avoid floats by default).
     LayoutUnit result = clearSet ? max<LayoutUnit>(0, logicalBottom - logicalTop) : LayoutUnit();
     if (!result && child.avoidsFloats()) {
         LayoutUnit newLogicalTop = logicalTop;
         while (true) {
             LayoutUnit availableLogicalWidthAtNewLogicalTopOffset = availableLogicalWidthForLine(newLogicalTop, false, logicalHeightForChild(child));
             if (availableLogicalWidthAtNewLogicalTopOffset == availableLogicalWidthForContent(newLogicalTop))
                 return newLogicalTop - logicalTop;

             RenderRegion* region = regionAtBlockOffset(logicalTopForChild(child));
             LayoutRect borderBox = child.borderBoxRectInRegion(region, DoNotCacheRenderBoxRegionInfo);
             LayoutUnit childLogicalWidthAtOldLogicalTopOffset = isHorizontalWritingMode() ? borderBox.width() : borderBox.height();

             // FIXME: None of this is right for perpendicular writing-mode children.
             LayoutUnit childOldLogicalWidth = child.logicalWidth();
             LayoutUnit childOldMarginLeft = child.marginLeft();
             LayoutUnit childOldMarginRight = child.marginRight();
             LayoutUnit childOldLogicalTop = child.logicalTop();

             child.setLogicalTop(newLogicalTop);
             child.updateLogicalWidth();
             region = regionAtBlockOffset(logicalTopForChild(child));
             borderBox = child.borderBoxRectInRegion(region, DoNotCacheRenderBoxRegionInfo);
             LayoutUnit childLogicalWidthAtNewLogicalTopOffset = isHorizontalWritingMode() ? borderBox.width() : borderBox.height();

             child.setLogicalTop(childOldLogicalTop);
             child.setLogicalWidth(childOldLogicalWidth);
             child.setMarginLeft(childOldMarginLeft);
             child.setMarginRight(childOldMarginRight);

             if (childLogicalWidthAtNewLogicalTopOffset <= availableLogicalWidthAtNewLogicalTopOffset) {
                 // Even though we may not be moving, if the logical width did shrink because of the presence of new floats, then
                 // we need to force a relayout as though we shifted. This happens because of the dynamic addition of overhanging floats
                 // from previous siblings when negative margins exist on a child (see the addOverhangingFloats call at the end of collapseMargins).
                 if (childLogicalWidthAtOldLogicalTopOffset != childLogicalWidthAtNewLogicalTopOffset)
                     child.setChildNeedsLayout(MarkOnlyThis);
                 return newLogicalTop - logicalTop;
             }

             newLogicalTop = nextFloatLogicalBottomBelow(newLogicalTop);
             ASSERT(newLogicalTop >= logicalTop);
             if (newLogicalTop < logicalTop)
                 break;
         }
         ASSERT_NOT_REACHED();
     }
     return result;
 }

 bool RenderBlockFlow::hitTestFloats(const HitTestRequest& request, HitTestResult& result, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset)
 {
     if (!m_floatingObjects)
         return false;

     LayoutPoint adjustedLocation = accumulatedOffset;
     if (isRenderView())
         adjustedLocation += toLayoutSize(toRenderView(*this).frameView().scrollPosition());

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     auto begin = floatingObjectSet.begin();
     for (auto it = floatingObjectSet.end(); it != begin;) {
         --it;
         FloatingObject* floatingObject = it->get();
         if (floatingObject->shouldPaint() && !floatingObject->renderer().hasSelfPaintingLayer()) {
             LayoutUnit xOffset = xPositionForFloatIncludingMargin(floatingObject) - floatingObject->renderer().x();
             LayoutUnit yOffset = yPositionForFloatIncludingMargin(floatingObject) - floatingObject->renderer().y();
             LayoutPoint childPoint = flipFloatForWritingModeForChild(floatingObject, adjustedLocation + LayoutSize(xOffset, yOffset));
             if (floatingObject->renderer().hitTest(request, result, locationInContainer, childPoint)) {
                 updateHitTestResult(result, locationInContainer.point() - toLayoutSize(childPoint));
                 return true;
             }
         }
     }

     return false;
 }

 bool RenderBlockFlow::hitTestInlineChildren(const HitTestRequest& request, HitTestResult& result, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction hitTestAction)
 {
     ASSERT(childrenInline());

     if (m_simpleLineLayout)
         return SimpleLineLayout::hitTestFlow(*this, *m_simpleLineLayout, request, result, locationInContainer, accumulatedOffset, hitTestAction);

     return m_lineBoxes.hitTest(this, request, result, locationInContainer, accumulatedOffset, hitTestAction);
 }

 void RenderBlockFlow::adjustForBorderFit(LayoutUnit x, LayoutUnit& left, LayoutUnit& right) const
 {
     if (style().visibility() != VISIBLE)
         return;

     // We don't deal with relative positioning.  Our assumption is that you shrink to fit the lines without accounting
     // for either overflow or translations via relative positioning.
     if (childrenInline()) {
         const_cast<RenderBlockFlow&>(*this).ensureLineBoxes();

         for (auto box = firstRootBox(); box; box = box->nextRootBox()) {
             if (box->firstChild())
                 left = min(left, x + static_cast<LayoutUnit>(box->firstChild()->x()));
             if (box->lastChild())
                 right = max(right, x + static_cast<LayoutUnit>(ceilf(box->lastChild()->logicalRight())));
         }
     } else {
         for (RenderBox* obj = firstChildBox(); obj; obj = obj->nextSiblingBox()) {
             if (!obj->isFloatingOrOutOfFlowPositioned()) {
                 if (obj->isRenderBlockFlow() && !obj->hasOverflowClip())
                     toRenderBlockFlow(obj)->adjustForBorderFit(x + obj->x(), left, right);
                 else if (obj->style().visibility() == VISIBLE) {
                     // We are a replaced element or some kind of non-block-flow object.
                     left = min(left, x + obj->x());
                     right = max(right, x + obj->x() + obj->width());
                 }
             }
         }
     }

     if (m_floatingObjects) {
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         auto end = floatingObjectSet.end();
         for (auto it = floatingObjectSet.begin(); it != end; ++it) {
             FloatingObject* r = it->get();
             // Only examine the object if our m_shouldPaint flag is set.
             if (r->shouldPaint()) {
                 LayoutUnit floatLeft = xPositionForFloatIncludingMargin(r) - r->renderer().x();
                 LayoutUnit floatRight = floatLeft + r->renderer().width();
                 left = min(left, floatLeft);
                 right = max(right, floatRight);
             }
         }
     }
 }

 void RenderBlockFlow::fitBorderToLinesIfNeeded()
 {
     if (style().borderFit() == BorderFitBorder || hasOverrideWidth())
         return;

     // Walk any normal flow lines to snugly fit.
     LayoutUnit left = LayoutUnit::max();
     LayoutUnit right = LayoutUnit::min();
     LayoutUnit oldWidth = contentWidth();
     adjustForBorderFit(0, left, right);

     // Clamp to our existing edges. We can never grow. We only shrink.
     LayoutUnit leftEdge = borderLeft() + paddingLeft();
     LayoutUnit rightEdge = leftEdge + oldWidth;
     left = min(rightEdge, max(leftEdge, left));
     right = max(leftEdge, min(rightEdge, right));

     LayoutUnit newContentWidth = right - left;
     if (newContentWidth == oldWidth)
         return;

     setOverrideLogicalContentWidth(newContentWidth);
     layoutBlock(false);
     clearOverrideLogicalContentWidth();
 }

 void RenderBlockFlow::markLinesDirtyInBlockRange(LayoutUnit logicalTop, LayoutUnit logicalBottom, RootInlineBox* highest)
 {
     if (logicalTop >= logicalBottom)
         return;

     RootInlineBox* lowestDirtyLine = lastRootBox();
     RootInlineBox* afterLowest = lowestDirtyLine;
     while (lowestDirtyLine && lowestDirtyLine->lineBottomWithLeading() >= logicalBottom && logicalBottom < LayoutUnit::max()) {
         afterLowest = lowestDirtyLine;
         lowestDirtyLine = lowestDirtyLine->prevRootBox();
     }

     while (afterLowest && afterLowest != highest && (afterLowest->lineBottomWithLeading() >= logicalTop || afterLowest->lineBottomWithLeading() < 0)) {
         afterLowest->markDirty();
         afterLowest = afterLowest->prevRootBox();
     }
 }

 int RenderBlockFlow::firstLineBaseline() const
 {
     if (isWritingModeRoot() && !isRubyRun())
         return -1;

     if (!childrenInline())
         return RenderBlock::firstLineBaseline();

     if (!hasLines())
         return -1;

     if (m_simpleLineLayout)
         return SimpleLineLayout::computeFlowFirstLineBaseline(*this, *m_simpleLineLayout);

     ASSERT(firstLineBox());
     return firstLineBox()->logicalTop() + firstLineStyle().fontMetrics().ascent(firstRootBox()->baselineType());
 }

 int RenderBlockFlow::inlineBlockBaseline(LineDirectionMode lineDirection) const
 {
     if (isWritingModeRoot() && !isRubyRun())
         return -1;

     if (!childrenInline())
         return RenderBlock::inlineBlockBaseline(lineDirection);

     if (!hasLines()) {
         if (!hasLineIfEmpty())
             return -1;
         const FontMetrics& fontMetrics = firstLineStyle().fontMetrics();
         return fontMetrics.ascent()
              + (lineHeight(true, lineDirection, PositionOfInteriorLineBoxes) - fontMetrics.height()) / 2
              + (lineDirection == HorizontalLine ? borderTop() + paddingTop() : borderRight() + paddingRight());
     }

     if (m_simpleLineLayout)
         return SimpleLineLayout::computeFlowLastLineBaseline(*this, *m_simpleLineLayout);

     bool isFirstLine = lastLineBox() == firstLineBox();
     const RenderStyle& style = isFirstLine ? firstLineStyle() : this->style();
     return lastLineBox()->logicalTop() + style.fontMetrics().ascent(lastRootBox()->baselineType());
 }

 GapRects RenderBlockFlow::inlineSelectionGaps(RenderBlock& rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
     LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const LogicalSelectionOffsetCaches& cache, const PaintInfo* paintInfo)
 {
     ASSERT(!m_simpleLineLayout);

     GapRects result;

     bool containsStart = selectionState() == SelectionStart || selectionState() == SelectionBoth;

     if (!hasLines()) {
         if (containsStart) {
             // Go ahead and update our lastLogicalTop to be the bottom of the block.  <hr>s or empty blocks with height can trip this
             // case.
             lastLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + logicalHeight();
             lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, logicalHeight(), cache);
             lastLogicalRight = logicalRightSelectionOffset(rootBlock, logicalHeight(), cache);
         }
         return result;
     }

     RootInlineBox* lastSelectedLine = 0;
     RootInlineBox* curr;
     for (curr = firstRootBox(); curr && !curr->hasSelectedChildren(); curr = curr->nextRootBox()) { }

     // Now paint the gaps for the lines.
     for (; curr && curr->hasSelectedChildren(); curr = curr->nextRootBox()) {
         LayoutUnit selTop =  curr->selectionTopAdjustedForPrecedingBlock();
         LayoutUnit selHeight = curr->selectionHeightAdjustedForPrecedingBlock();

         if (!containsStart && !lastSelectedLine &&
             selectionState() != SelectionStart && selectionState() != SelectionBoth)
             result.uniteCenter(blockSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop, lastLogicalLeft, lastLogicalRight, selTop, cache, paintInfo));

         LayoutRect logicalRect(curr->logicalLeft(), selTop, curr->logicalWidth(), selTop + selHeight);
         logicalRect.move(isHorizontalWritingMode() ? offsetFromRootBlock : offsetFromRootBlock.transposedSize());
         LayoutRect physicalRect = rootBlock.logicalRectToPhysicalRect(rootBlockPhysicalPosition, logicalRect);
         if (!paintInfo || (isHorizontalWritingMode() && physicalRect.y() < paintInfo->rect.maxY() && physicalRect.maxY() > paintInfo->rect.y())
             || (!isHorizontalWritingMode() && physicalRect.x() < paintInfo->rect.maxX() && physicalRect.maxX() > paintInfo->rect.x()))
             result.unite(curr->lineSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, selTop, selHeight, cache, paintInfo));

         lastSelectedLine = curr;
     }

     if (containsStart && !lastSelectedLine)
         // VisibleSelection must start just after our last line.
         lastSelectedLine = lastRootBox();

     if (lastSelectedLine && selectionState() != SelectionEnd && selectionState() != SelectionBoth) {
         // Go ahead and update our lastY to be the bottom of the last selected line.
         lastLogicalTop = blockDirectionOffset(rootBlock, offsetFromRootBlock) + lastSelectedLine->selectionBottom();
         lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, lastSelectedLine->selectionBottom(), cache);
         lastLogicalRight = logicalRightSelectionOffset(rootBlock, lastSelectedLine->selectionBottom(), cache);
     }
     return result;
 }

 void RenderBlockFlow::createRenderNamedFlowFragmentIfNeeded()
 {
     if (!document().cssRegionsEnabled() || renderNamedFlowFragment() || isRenderNamedFlowFragment())
         return;

     if (style().isDisplayRegionType() && style().hasFlowFrom()) {
         RenderNamedFlowFragment* flowFragment = new RenderNamedFlowFragment(document(), RenderNamedFlowFragment::createStyle(style()));
         flowFragment->initializeStyle();
         setRenderNamedFlowFragment(flowFragment);
         addChild(renderNamedFlowFragment());
     }
 }

 bool RenderBlockFlow::canHaveChildren() const
 {
     return !renderNamedFlowFragment() ? RenderBlock::canHaveChildren() : renderNamedFlowFragment()->canHaveChildren();
 }

 bool RenderBlockFlow::canHaveGeneratedChildren() const
 {
     return !renderNamedFlowFragment() ? RenderBlock::canHaveGeneratedChildren() : renderNamedFlowFragment()->canHaveGeneratedChildren();
 }

 bool RenderBlockFlow::namedFlowFragmentNeedsUpdate() const
 {
     if (!isRenderNamedFlowFragmentContainer())
         return false;

     return hasRelativeLogicalHeight() && !isRenderView();
 }

 void RenderBlockFlow::updateLogicalHeight()
 {
     RenderBlock::updateLogicalHeight();

     if (renderNamedFlowFragment())
         renderNamedFlowFragment()->setLogicalHeight(max<LayoutUnit>(0, logicalHeight() - borderAndPaddingLogicalHeight()));
 }

 void RenderBlockFlow::setRenderNamedFlowFragment(RenderNamedFlowFragment* flowFragment)
 {
     RenderBlockFlowRareData& rareData = ensureRareData();
     if (rareData.m_renderNamedFlowFragment)
         rareData.m_renderNamedFlowFragment->destroy();
     rareData.m_renderNamedFlowFragment = flowFragment;
 }

 // FIXME: Use this function in more places.
 RenderBlockFlow::RenderBlockFlowRareData& RenderBlockFlow::ensureRareData()
 {
     if (m_rareData)
         return *m_rareData;

     m_rareData = adoptPtr(new RenderBlockFlowRareData(*this));
     return *m_rareData;
 }

 static bool shouldCheckLines(RenderObject& obj)
 {
     return !obj.isFloatingOrOutOfFlowPositioned() && !obj.isRunIn() && obj.isRenderBlockFlow() && obj.style().height().isAuto() && (!obj.isDeprecatedFlexibleBox() || obj.style().boxOrient() == VERTICAL);
 }

 RootInlineBox* RenderBlockFlow::lineAtIndex(int i) const
 {
     ASSERT(i >= 0);

     if (style().visibility() != VISIBLE)
         return nullptr;

     if (childrenInline()) {
         for (auto box = firstRootBox(); box; box = box->nextRootBox()) {
             if (!i--)
                 return box;
         }
     } else {
         for (auto child = firstChild(); child; child = child->nextSibling()) {
             if (!shouldCheckLines(*child))
                 continue;
             if (RootInlineBox* box = toRenderBlockFlow(child)->lineAtIndex(i))
                 return box;
         }
     }

     return nullptr;
 }

 int RenderBlockFlow::lineCount(const RootInlineBox* stopRootInlineBox, bool* found) const
 {
     if (style().visibility() != VISIBLE)
         return 0;

     int count = 0;

     if (childrenInline()) {
         for (auto box = firstRootBox(); box; box = box->nextRootBox()) {
             count++;
             if (box == stopRootInlineBox) {
                 if (found)
                     *found = true;
                 break;
             }
         }
     } else {
         for (auto child = firstChild(); child; child = child->nextSibling()) {
             if (shouldCheckLines(*child)) {
                 bool recursiveFound = false;
                 count += toRenderBlockFlow(child)->lineCount(stopRootInlineBox, &recursiveFound);
                 if (recursiveFound) {
                     if (found)
                         *found = true;
                     break;
                 }
             }
         }
     }

     return count;
 }

 static int getHeightForLineCount(const RenderBlockFlow& block, int lineCount, bool includeBottom, int& count)
 {
     if (block.style().visibility() != VISIBLE)
         return -1;

     if (block.childrenInline()) {
         for (auto box = block.firstRootBox(); box; box = box->nextRootBox()) {
             if (++count == lineCount)
                 return box->lineBottom() + (includeBottom ? (block.borderBottom() + block.paddingBottom()) : LayoutUnit());
         }
     } else {
         RenderBox* normalFlowChildWithoutLines = 0;
         for (auto obj = block.firstChildBox(); obj; obj = obj->nextSiblingBox()) {
             if (shouldCheckLines(*obj)) {
                 int result = getHeightForLineCount(toRenderBlockFlow(*obj), lineCount, false, count);
                 if (result != -1)
                     return result + obj->y() + (includeBottom ? (block.borderBottom() + block.paddingBottom()) : LayoutUnit());
             } else if (!obj->isFloatingOrOutOfFlowPositioned() && !obj->isRunIn())
                 normalFlowChildWithoutLines = obj;
         }
         if (normalFlowChildWithoutLines && !lineCount)
             return normalFlowChildWithoutLines->y() + normalFlowChildWithoutLines->height();
     }

     return -1;
 }

 int RenderBlockFlow::heightForLineCount(int lineCount)
 {
     int count = 0;
     return getHeightForLineCount(*this, lineCount, true, count);
 }

 void RenderBlockFlow::clearTruncation()
 {
     if (style().visibility() != VISIBLE)
         return;

     if (childrenInline() && hasMarkupTruncation()) {
         ensureLineBoxes();

         setHasMarkupTruncation(false);
         for (auto box = firstRootBox(); box; box = box->nextRootBox())
             box->clearTruncation();
     } else {
         for (auto child = firstChild(); child; child = child->nextSibling()) {
             if (shouldCheckLines(*child))
                 toRenderBlockFlow(child)->clearTruncation();
         }
     }
 }

 bool RenderBlockFlow::containsNonZeroBidiLevel() const
 {
     for (auto root = firstRootBox(); root; root = root->nextRootBox()) {
         for (auto box = root->firstLeafChild(); box; box = box->nextLeafChild()) {
             if (box->bidiLevel())
                 return true;
         }
     }
     return false;
 }

 Position RenderBlockFlow::positionForBox(InlineBox *box, bool start) const
 {
     if (!box)
         return Position();

     if (!box->renderer().nonPseudoNode())
         return createLegacyEditingPosition(nonPseudoElement(), start ? caretMinOffset() : caretMaxOffset());

     if (!box->isInlineTextBox())
         return createLegacyEditingPosition(box->renderer().nonPseudoNode(), start ? box->renderer().caretMinOffset() : box->renderer().caretMaxOffset());

     InlineTextBox* textBox = toInlineTextBox(box);
     return createLegacyEditingPosition(box->renderer().nonPseudoNode(), start ? textBox->start() : textBox->start() + textBox->len());
 }

 VisiblePosition RenderBlockFlow::positionForPointWithInlineChildren(const LayoutPoint& pointInLogicalContents)
 {
     ASSERT(childrenInline());

     ensureLineBoxes();

     if (!firstRootBox())
         return createVisiblePosition(0, DOWNSTREAM);

     bool linesAreFlipped = style().isFlippedLinesWritingMode();
     bool blocksAreFlipped = style().isFlippedBlocksWritingMode();

     // look for the closest line box in the root box which is at the passed-in y coordinate
     InlineBox* closestBox = 0;
     RootInlineBox* firstRootBoxWithChildren = 0;
     RootInlineBox* lastRootBoxWithChildren = 0;
     for (RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox()) {
         if (!root->firstLeafChild())
             continue;
         if (!firstRootBoxWithChildren)
             firstRootBoxWithChildren = root;

         if (!linesAreFlipped && root->isFirstAfterPageBreak() && (pointInLogicalContents.y() < root->lineTopWithLeading()
             || (blocksAreFlipped && pointInLogicalContents.y() == root->lineTopWithLeading())))
             break;

         lastRootBoxWithChildren = root;

         // check if this root line box is located at this y coordinate
         if (pointInLogicalContents.y() < root->selectionBottom() || (blocksAreFlipped && pointInLogicalContents.y() == root->selectionBottom())) {
             if (linesAreFlipped) {
                 RootInlineBox* nextRootBoxWithChildren = root->nextRootBox();
                 while (nextRootBoxWithChildren && !nextRootBoxWithChildren->firstLeafChild())
                     nextRootBoxWithChildren = nextRootBoxWithChildren->nextRootBox();

                 if (nextRootBoxWithChildren && nextRootBoxWithChildren->isFirstAfterPageBreak() && (pointInLogicalContents.y() > nextRootBoxWithChildren->lineTopWithLeading()
                     || (!blocksAreFlipped && pointInLogicalContents.y() == nextRootBoxWithChildren->lineTopWithLeading())))
                     continue;
             }
             closestBox = root->closestLeafChildForLogicalLeftPosition(pointInLogicalContents.x());
             if (closestBox)
                 break;
         }
     }

     bool moveCaretToBoundary = frame().editor().behavior().shouldMoveCaretToHorizontalBoundaryWhenPastTopOrBottom();

     if (!moveCaretToBoundary && !closestBox && lastRootBoxWithChildren) {
         // y coordinate is below last root line box, pretend we hit it
         closestBox = lastRootBoxWithChildren->closestLeafChildForLogicalLeftPosition(pointInLogicalContents.x());
     }

     if (closestBox) {
         if (moveCaretToBoundary) {
             LayoutUnit firstRootBoxWithChildrenTop = min<LayoutUnit>(firstRootBoxWithChildren->selectionTop(), firstRootBoxWithChildren->logicalTop());
             if (pointInLogicalContents.y() < firstRootBoxWithChildrenTop
                 || (blocksAreFlipped && pointInLogicalContents.y() == firstRootBoxWithChildrenTop)) {
                 InlineBox* box = firstRootBoxWithChildren->firstLeafChild();
                 if (box->isLineBreak()) {
                     if (InlineBox* newBox = box->nextLeafChildIgnoringLineBreak())
                         box = newBox;
                 }
                 // y coordinate is above first root line box, so return the start of the first
                 return VisiblePosition(positionForBox(box, true), DOWNSTREAM);
             }
         }

         // pass the box a top position that is inside it
         LayoutPoint point(pointInLogicalContents.x(), closestBox->root().blockDirectionPointInLine());
         if (!isHorizontalWritingMode())
             point = point.transposedPoint();
         if (closestBox->renderer().isReplaced())
             return positionForPointRespectingEditingBoundaries(*this, toRenderBox(closestBox->renderer()), point);
         return closestBox->renderer().positionForPoint(point);
     }

     if (lastRootBoxWithChildren) {
         // We hit this case for Mac behavior when the Y coordinate is below the last box.
         ASSERT(moveCaretToBoundary);
         InlineBox* logicallyLastBox;
         if (lastRootBoxWithChildren->getLogicalEndBoxWithNode(logicallyLastBox))
             return VisiblePosition(positionForBox(logicallyLastBox, false), DOWNSTREAM);
     }

     // Can't reach this. We have a root line box, but it has no kids.
     // FIXME: This should ASSERT_NOT_REACHED(), but clicking on placeholder text
     // seems to hit this code path.
     return createVisiblePosition(0, DOWNSTREAM);
 }

 void RenderBlockFlow::addFocusRingRectsForInlineChildren(Vector<IntRect>& rects, const LayoutPoint& additionalOffset, const RenderLayerModelObject*)
 {
     ASSERT(childrenInline());

     ensureLineBoxes();

     for (RootInlineBox* curr = firstRootBox(); curr; curr = curr->nextRootBox()) {
         LayoutUnit top = max<LayoutUnit>(curr->lineTop(), curr->top());
         LayoutUnit bottom = min<LayoutUnit>(curr->lineBottom(), curr->top() + curr->height());
         LayoutRect rect(additionalOffset.x() + curr->x(), additionalOffset.y() + top, curr->width(), bottom - top);
         if (!rect.isEmpty())
             rects.append(pixelSnappedIntRect(rect));
     }
 }

 void RenderBlockFlow::paintInlineChildren(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
     ASSERT(childrenInline());

     if (m_simpleLineLayout) {
         SimpleLineLayout::paintFlow(*this, *m_simpleLineLayout, paintInfo, paintOffset);
         return;
     }
     m_lineBoxes.paint(this, paintInfo, paintOffset);
 }

 bool RenderBlockFlow::relayoutForPagination(bool hasSpecifiedPageLogicalHeight, LayoutUnit pageLogicalHeight, LayoutStateMaintainer& statePusher)
 {
     if (!hasColumns())
         return false;

     OwnPtr<RenderOverflow> savedOverflow = m_overflow.release();
     if (childrenInline())
         addOverflowFromInlineChildren();
     else
         addOverflowFromBlockChildren();
     LayoutUnit layoutOverflowLogicalBottom = (isHorizontalWritingMode() ? layoutOverflowRect().maxY() : layoutOverflowRect().maxX()) - borderAndPaddingBefore();

     // FIXME: We don't balance properly at all in the presence of forced page breaks.  We need to understand what
     // the distance between forced page breaks is so that we can avoid making the minimum column height too tall.
     ColumnInfo* colInfo = columnInfo();
     if (!hasSpecifiedPageLogicalHeight) {
         LayoutUnit columnHeight = pageLogicalHeight;
         int minColumnCount = colInfo->forcedBreaks() + 1;
         int desiredColumnCount = colInfo->desiredColumnCount();
         if (minColumnCount >= desiredColumnCount) {
             // The forced page breaks are in control of the balancing.  Just set the column height to the
             // maximum page break distance.
             if (!pageLogicalHeight) {
                 LayoutUnit distanceBetweenBreaks = max<LayoutUnit>(colInfo->maximumDistanceBetweenForcedBreaks(),
                     view().layoutState()->pageLogicalOffset(this, borderAndPaddingBefore() + layoutOverflowLogicalBottom) - colInfo->forcedBreakOffset());
                 columnHeight = max(colInfo->minimumColumnHeight(), distanceBetweenBreaks);
             }
         } else if (layoutOverflowLogicalBottom > boundedMultiply(pageLogicalHeight, desiredColumnCount)) {
             // Now that we know the intrinsic height of the columns, we have to rebalance them.
             columnHeight = max<LayoutUnit>(colInfo->minimumColumnHeight(), ceilf((float)layoutOverflowLogicalBottom / desiredColumnCount));
         }

         if (columnHeight && columnHeight != pageLogicalHeight) {
             statePusher.pop();
             setEverHadLayout(true);
             layoutBlock(false, columnHeight);
             return true;
         }
     }

     if (pageLogicalHeight)
         colInfo->setColumnCountAndHeight(ceilf((float)layoutOverflowLogicalBottom / pageLogicalHeight), pageLogicalHeight);

     if (columnCount(colInfo)) {
         setLogicalHeight(borderAndPaddingBefore() + colInfo->columnHeight() + borderAndPaddingAfter() + scrollbarLogicalHeight());
         clearOverflow();
     } else
         m_overflow = savedOverflow.release();

     return false;
 }

 bool RenderBlockFlow::hasLines() const
 {
     ASSERT(childrenInline());

     if (m_simpleLineLayout)
         return m_simpleLineLayout->lineCount();

     return lineBoxes().firstLineBox();
 }

 void RenderBlockFlow::layoutSimpleLines(LayoutUnit& repaintLogicalTop, LayoutUnit& repaintLogicalBottom)
 {
     ASSERT(!m_lineBoxes.firstLineBox());

     m_simpleLineLayout = SimpleLineLayout::create(*this);

     LayoutUnit lineLayoutHeight = SimpleLineLayout::computeFlowHeight(*this, *m_simpleLineLayout);
     LayoutUnit lineLayoutTop = borderAndPaddingBefore();

     repaintLogicalTop = lineLayoutTop;
     repaintLogicalBottom = lineLayoutTop + lineLayoutHeight;

     setLogicalHeight(lineLayoutTop + lineLayoutHeight + borderAndPaddingAfter());
 }

 void RenderBlockFlow::deleteLineBoxesBeforeSimpleLineLayout()
 {
     ASSERT(m_lineLayoutPath == SimpleLinesPath);
     lineBoxes().deleteLineBoxes();
     toRenderText(firstChild())->deleteLineBoxesBeforeSimpleLineLayout();
 }

 void RenderBlockFlow::ensureLineBoxes()
 {
     m_lineLayoutPath = ForceLineBoxesPath;

     if (!m_simpleLineLayout)
         return;
     m_simpleLineLayout = nullptr;

 #if !ASSERT_DISABLED
     LayoutUnit oldHeight = logicalHeight();
 #endif
     bool didNeedLayout = needsLayout();

     bool relayoutChildren = false;
     LayoutUnit repaintLogicalTop;
     LayoutUnit repaintLogicalBottom;
     layoutLineBoxes(relayoutChildren, repaintLogicalTop, repaintLogicalBottom);

     updateLogicalHeight();
     ASSERT(didNeedLayout || logicalHeight() == oldHeight);

     if (!didNeedLayout)
         clearNeedsLayout();
 }

 #ifndef NDEBUG
 void RenderBlockFlow::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const RenderObject* obj) const
 {
     RenderBlock::showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj);
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 #endif

 } // namespace WebCore