Source/WebCore/dom/NodeRareData.h - WebKit - Git at Google

 /*
  * Copyright (C) 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 David Smith <catfish.man@gmail.com>
  *
  * 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.
  *
  */

 #pragma once

 #include "ChildNodeList.h"
 #include "HTMLCollection.h"
 #include "HTMLNames.h"
 #include "LiveNodeList.h"
 #include "MutationObserverRegistration.h"
 #include "Page.h"
 #include "QualifiedName.h"
 #include "TagCollection.h"
 #include <wtf/HashSet.h>
 #include <wtf/text/AtomicString.h>

 namespace WebCore {

 class LabelsNodeList;
 class NameNodeList;
 class RadioNodeList;
 class TreeScope;

 template <class ListType> struct NodeListTypeIdentifier;
 template <> struct NodeListTypeIdentifier<NameNodeList> { static int value() { return 0; } };
 template <> struct NodeListTypeIdentifier<RadioNodeList> { static int value() { return 1; } };
 template <> struct NodeListTypeIdentifier<LabelsNodeList> { static int value() { return 2; } };

 class NodeListsNodeData {
     WTF_MAKE_NONCOPYABLE(NodeListsNodeData); WTF_MAKE_FAST_ALLOCATED;
 public:
     NodeListsNodeData()
         : m_childNodeList(nullptr)
         , m_emptyChildNodeList(nullptr)
     {
     }

     void clearChildNodeListCache()
     {
         if (m_childNodeList)
             m_childNodeList->invalidateCache();
     }

     Ref<ChildNodeList> ensureChildNodeList(ContainerNode& node)
     {
         ASSERT(!m_emptyChildNodeList);
         if (m_childNodeList)
             return *m_childNodeList;
         auto list = ChildNodeList::create(node);
         m_childNodeList = list.ptr();
         return list;
     }

     void removeChildNodeList(ChildNodeList* list)
     {
         ASSERT(m_childNodeList == list);
         if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(list->ownerNode()))
             return;
         m_childNodeList = nullptr;
     }

     Ref<EmptyNodeList> ensureEmptyChildNodeList(Node& node)
     {
         ASSERT(!m_childNodeList);
         if (m_emptyChildNodeList)
             return *m_emptyChildNodeList;
         auto list = EmptyNodeList::create(node);
         m_emptyChildNodeList = list.ptr();
         return list;
     }

     void removeEmptyChildNodeList(EmptyNodeList* list)
     {
         ASSERT(m_emptyChildNodeList == list);
         if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(list->ownerNode()))
             return;
         m_emptyChildNodeList = nullptr;
     }

     struct NodeListCacheMapEntryHash {
         static unsigned hash(const std::pair<unsigned char, AtomicString>& entry)
         {
             return DefaultHash<AtomicString>::Hash::hash(entry.second) + entry.first;
         }
         static bool equal(const std::pair<unsigned char, AtomicString>& a, const std::pair<unsigned char, AtomicString>& b) { return a.first == b.first && DefaultHash<AtomicString>::Hash::equal(a.second, b.second); }
         static const bool safeToCompareToEmptyOrDeleted = DefaultHash<AtomicString>::Hash::safeToCompareToEmptyOrDeleted;
     };

     typedef HashMap<std::pair<unsigned char, AtomicString>, LiveNodeList*, NodeListCacheMapEntryHash> NodeListAtomicNameCacheMap;
     typedef HashMap<std::pair<unsigned char, AtomicString>, HTMLCollection*, NodeListCacheMapEntryHash> CollectionCacheMap;
     typedef HashMap<QualifiedName, TagCollectionNS*> TagCollectionNSCache;

     template<typename T, typename ContainerType>
     ALWAYS_INLINE Ref<T> addCacheWithAtomicName(ContainerType& container, const AtomicString& name)
     {
         NodeListAtomicNameCacheMap::AddResult result = m_atomicNameCaches.fastAdd(namedNodeListKey<T>(name), nullptr);
         if (!result.isNewEntry)
             return static_cast<T&>(*result.iterator->value);

         auto list = T::create(container, name);
         result.iterator->value = &list.get();
         return list;
     }

     ALWAYS_INLINE Ref<TagCollectionNS> addCachedTagCollectionNS(ContainerNode& node, const AtomicString& namespaceURI, const AtomicString& localName)
     {
         QualifiedName name(nullAtom(), localName, namespaceURI);
         TagCollectionNSCache::AddResult result = m_tagCollectionNSCache.fastAdd(name, nullptr);
         if (!result.isNewEntry)
             return *result.iterator->value;

         auto list = TagCollectionNS::create(node, namespaceURI, localName);
         result.iterator->value = list.ptr();
         return list;
     }

     template<typename T, typename ContainerType>
     ALWAYS_INLINE Ref<T> addCachedCollection(ContainerType& container, CollectionType collectionType, const AtomicString& name)
     {
         CollectionCacheMap::AddResult result = m_cachedCollections.fastAdd(namedCollectionKey(collectionType, name), nullptr);
         if (!result.isNewEntry)
             return static_cast<T&>(*result.iterator->value);

         auto list = T::create(container, collectionType, name);
         result.iterator->value = &list.get();
         return list;
     }

     template<typename T, typename ContainerType>
     ALWAYS_INLINE Ref<T> addCachedCollection(ContainerType& container, CollectionType collectionType)
     {
         CollectionCacheMap::AddResult result = m_cachedCollections.fastAdd(namedCollectionKey(collectionType, starAtom()), nullptr);
         if (!result.isNewEntry)
             return static_cast<T&>(*result.iterator->value);

         auto list = T::create(container, collectionType);
         result.iterator->value = &list.get();
         return list;
     }

     template<typename T>
     T* cachedCollection(CollectionType collectionType)
     {
         return static_cast<T*>(m_cachedCollections.get(namedCollectionKey(collectionType, starAtom())));
     }

     template <class NodeListType>
     void removeCacheWithAtomicName(NodeListType* list, const AtomicString& name = starAtom())
     {
         ASSERT(list == m_atomicNameCaches.get(namedNodeListKey<NodeListType>(name)));
         if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(list->ownerNode()))
             return;
         m_atomicNameCaches.remove(namedNodeListKey<NodeListType>(name));
     }

     void removeCachedTagCollectionNS(HTMLCollection& collection, const AtomicString& namespaceURI, const AtomicString& localName)
     {
         QualifiedName name(nullAtom(), localName, namespaceURI);
         ASSERT(&collection == m_tagCollectionNSCache.get(name));
         if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(collection.ownerNode()))
             return;
         m_tagCollectionNSCache.remove(name);
     }

     void removeCachedCollection(HTMLCollection* collection, const AtomicString& name = starAtom())
     {
         ASSERT(collection == m_cachedCollections.get(namedCollectionKey(collection->type(), name)));
         if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(collection->ownerNode()))
             return;
         m_cachedCollections.remove(namedCollectionKey(collection->type(), name));
     }

     void invalidateCaches();
     void invalidateCachesForAttribute(const QualifiedName& attrName);

     void adoptTreeScope()
     {
         invalidateCaches();
     }

     void adoptDocument(Document& oldDocument, Document& newDocument)
     {
         if (&oldDocument == &newDocument) {
             invalidateCaches();
             return;
         }

         for (auto& cache : m_atomicNameCaches.values())
             cache->invalidateCacheForDocument(oldDocument);

         for (auto& list : m_tagCollectionNSCache.values()) {
             ASSERT(!list->isRootedAtDocument());
             list->invalidateCacheForDocument(oldDocument);
         }

         for (auto& collection : m_cachedCollections.values())
             collection->invalidateCacheForDocument(oldDocument);
     }

 private:
     std::pair<unsigned char, AtomicString> namedCollectionKey(CollectionType type, const AtomicString& name)
     {
         return std::pair<unsigned char, AtomicString>(type, name);
     }

     template <class NodeListType>
     std::pair<unsigned char, AtomicString> namedNodeListKey(const AtomicString& name)
     {
         return std::pair<unsigned char, AtomicString>(NodeListTypeIdentifier<NodeListType>::value(), name);
     }

     bool deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(Node&);

     // These two are currently mutually exclusive and could be unioned. Not very important as this class is large anyway.
     ChildNodeList* m_childNodeList;
     EmptyNodeList* m_emptyChildNodeList;

     NodeListAtomicNameCacheMap m_atomicNameCaches;
     TagCollectionNSCache m_tagCollectionNSCache;
     CollectionCacheMap m_cachedCollections;
 };

 class NodeMutationObserverData {
     WTF_MAKE_NONCOPYABLE(NodeMutationObserverData); WTF_MAKE_FAST_ALLOCATED;
 public:
     Vector<std::unique_ptr<MutationObserverRegistration>> registry;
     HashSet<MutationObserverRegistration*> transientRegistry;

     NodeMutationObserverData() { }
 };

 class NodeRareData : public NodeRareDataBase {
     WTF_MAKE_NONCOPYABLE(NodeRareData); WTF_MAKE_FAST_ALLOCATED;
 public:
     NodeRareData(RenderObject* renderer)
         : NodeRareDataBase(renderer)
         , m_connectedFrameCount(0)
     { }

     void clearNodeLists() { m_nodeLists = nullptr; }
     NodeListsNodeData* nodeLists() const { return m_nodeLists.get(); }
     NodeListsNodeData& ensureNodeLists()
     {
         if (!m_nodeLists)
             m_nodeLists = std::make_unique<NodeListsNodeData>();
         return *m_nodeLists;
     }

     NodeMutationObserverData* mutationObserverData() { return m_mutationObserverData.get(); }
     NodeMutationObserverData& ensureMutationObserverData()
     {
         if (!m_mutationObserverData)
             m_mutationObserverData = std::make_unique<NodeMutationObserverData>();
         return *m_mutationObserverData;
     }

     unsigned connectedSubframeCount() const { return m_connectedFrameCount; }
     void incrementConnectedSubframeCount(unsigned amount)
     {
         m_connectedFrameCount += amount;
     }
     void decrementConnectedSubframeCount(unsigned amount)
     {
         ASSERT(m_connectedFrameCount);
         ASSERT(amount <= m_connectedFrameCount);
         m_connectedFrameCount -= amount;
     }

 private:
     unsigned m_connectedFrameCount : 10; // Must fit Page::maxNumberOfFrames.

     std::unique_ptr<NodeListsNodeData> m_nodeLists;
     std::unique_ptr<NodeMutationObserverData> m_mutationObserverData;
 };

 inline bool NodeListsNodeData::deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(Node& ownerNode)
 {
     ASSERT(ownerNode.nodeLists() == this);
     if ((m_childNodeList ? 1 : 0) + (m_emptyChildNodeList ? 1 : 0) + m_atomicNameCaches.size()
         + m_tagCollectionNSCache.size() + m_cachedCollections.size() != 1)
         return false;
     ownerNode.clearNodeLists();
     return true;
 }

 inline NodeRareData* Node::rareData() const
 {
     ASSERT_WITH_SECURITY_IMPLICATION(hasRareData());
     return static_cast<NodeRareData*>(m_data.m_rareData);
 }

 inline NodeRareData& Node::ensureRareData()
 {
     if (!hasRareData())
         materializeRareData();
     return *rareData();
 }

 // Ensure the 10 bits reserved for the m_connectedFrameCount cannot overflow
 static_assert(Page::maxNumberOfFrames < 1024, "Frame limit should fit in rare data count");

 } // namespace WebCore
	/*
	* Copyright (C) 2008, 2010 Apple Inc. All rights reserved.
	* Copyright (C) 2008 David Smith <catfish.man@gmail.com>
	*
	* 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.
	*
	*/

	#pragma once

	#include "ChildNodeList.h"
	#include "HTMLCollection.h"
	#include "HTMLNames.h"
	#include "LiveNodeList.h"
	#include "MutationObserverRegistration.h"
	#include "Page.h"
	#include "QualifiedName.h"
	#include "TagCollection.h"
	#include <wtf/HashSet.h>
	#include <wtf/text/AtomicString.h>

	namespace WebCore {

	class LabelsNodeList;
	class NameNodeList;
	class RadioNodeList;
	class TreeScope;

	template <class ListType> struct NodeListTypeIdentifier;
	template <> struct NodeListTypeIdentifier<NameNodeList> { static int value() { return 0; } };
	template <> struct NodeListTypeIdentifier<RadioNodeList> { static int value() { return 1; } };
	template <> struct NodeListTypeIdentifier<LabelsNodeList> { static int value() { return 2; } };

	class NodeListsNodeData {
	WTF_MAKE_NONCOPYABLE(NodeListsNodeData); WTF_MAKE_FAST_ALLOCATED;
	public:
	NodeListsNodeData()
	: m_childNodeList(nullptr)
	, m_emptyChildNodeList(nullptr)
	{
	}

	void clearChildNodeListCache()
	{
	if (m_childNodeList)
	m_childNodeList->invalidateCache();
	}

	Ref<ChildNodeList> ensureChildNodeList(ContainerNode& node)
	{
	ASSERT(!m_emptyChildNodeList);
	if (m_childNodeList)
	return *m_childNodeList;
	auto list = ChildNodeList::create(node);
	m_childNodeList = list.ptr();
	return list;
	}

	void removeChildNodeList(ChildNodeList* list)
	{
	ASSERT(m_childNodeList == list);
	if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(list->ownerNode()))
	return;
	m_childNodeList = nullptr;
	}

	Ref<EmptyNodeList> ensureEmptyChildNodeList(Node& node)
	{
	ASSERT(!m_childNodeList);
	if (m_emptyChildNodeList)
	return *m_emptyChildNodeList;
	auto list = EmptyNodeList::create(node);
	m_emptyChildNodeList = list.ptr();
	return list;
	}

	void removeEmptyChildNodeList(EmptyNodeList* list)
	{
	ASSERT(m_emptyChildNodeList == list);
	if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(list->ownerNode()))
	return;
	m_emptyChildNodeList = nullptr;
	}

	struct NodeListCacheMapEntryHash {
	static unsigned hash(const std::pair<unsigned char, AtomicString>& entry)
	{
	return DefaultHash<AtomicString>::Hash::hash(entry.second) + entry.first;
	}
	static bool equal(const std::pair<unsigned char, AtomicString>& a, const std::pair<unsigned char, AtomicString>& b) { return a.first == b.first && DefaultHash<AtomicString>::Hash::equal(a.second, b.second); }
	static const bool safeToCompareToEmptyOrDeleted = DefaultHash<AtomicString>::Hash::safeToCompareToEmptyOrDeleted;
	};

	typedef HashMap<std::pair<unsigned char, AtomicString>, LiveNodeList*, NodeListCacheMapEntryHash> NodeListAtomicNameCacheMap;
	typedef HashMap<std::pair<unsigned char, AtomicString>, HTMLCollection*, NodeListCacheMapEntryHash> CollectionCacheMap;
	typedef HashMap<QualifiedName, TagCollectionNS*> TagCollectionNSCache;

	template<typename T, typename ContainerType>
	ALWAYS_INLINE Ref<T> addCacheWithAtomicName(ContainerType& container, const AtomicString& name)
	{
	NodeListAtomicNameCacheMap::AddResult result = m_atomicNameCaches.fastAdd(namedNodeListKey<T>(name), nullptr);
	if (!result.isNewEntry)
	return static_cast<T&>(*result.iterator->value);

	auto list = T::create(container, name);
	result.iterator->value = &list.get();
	return list;
	}

	ALWAYS_INLINE Ref<TagCollectionNS> addCachedTagCollectionNS(ContainerNode& node, const AtomicString& namespaceURI, const AtomicString& localName)
	{
	QualifiedName name(nullAtom(), localName, namespaceURI);
	TagCollectionNSCache::AddResult result = m_tagCollectionNSCache.fastAdd(name, nullptr);
	if (!result.isNewEntry)
	return *result.iterator->value;

	auto list = TagCollectionNS::create(node, namespaceURI, localName);
	result.iterator->value = list.ptr();
	return list;
	}

	template<typename T, typename ContainerType>
	ALWAYS_INLINE Ref<T> addCachedCollection(ContainerType& container, CollectionType collectionType, const AtomicString& name)
	{
	CollectionCacheMap::AddResult result = m_cachedCollections.fastAdd(namedCollectionKey(collectionType, name), nullptr);
	if (!result.isNewEntry)
	return static_cast<T&>(*result.iterator->value);

	auto list = T::create(container, collectionType, name);
	result.iterator->value = &list.get();
	return list;
	}

	template<typename T, typename ContainerType>
	ALWAYS_INLINE Ref<T> addCachedCollection(ContainerType& container, CollectionType collectionType)
	{
	CollectionCacheMap::AddResult result = m_cachedCollections.fastAdd(namedCollectionKey(collectionType, starAtom()), nullptr);
	if (!result.isNewEntry)
	return static_cast<T&>(*result.iterator->value);

	auto list = T::create(container, collectionType);
	result.iterator->value = &list.get();
	return list;
	}

	template<typename T>
	T* cachedCollection(CollectionType collectionType)
	{
	return static_cast<T*>(m_cachedCollections.get(namedCollectionKey(collectionType, starAtom())));
	}

	template <class NodeListType>
	void removeCacheWithAtomicName(NodeListType* list, const AtomicString& name = starAtom())
	{
	ASSERT(list == m_atomicNameCaches.get(namedNodeListKey<NodeListType>(name)));
	if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(list->ownerNode()))
	return;
	m_atomicNameCaches.remove(namedNodeListKey<NodeListType>(name));
	}

	void removeCachedTagCollectionNS(HTMLCollection& collection, const AtomicString& namespaceURI, const AtomicString& localName)
	{
	QualifiedName name(nullAtom(), localName, namespaceURI);
	ASSERT(&collection == m_tagCollectionNSCache.get(name));
	if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(collection.ownerNode()))
	return;
	m_tagCollectionNSCache.remove(name);
	}

	void removeCachedCollection(HTMLCollection* collection, const AtomicString& name = starAtom())
	{
	ASSERT(collection == m_cachedCollections.get(namedCollectionKey(collection->type(), name)));
	if (deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(collection->ownerNode()))
	return;
	m_cachedCollections.remove(namedCollectionKey(collection->type(), name));
	}

	void invalidateCaches();
	void invalidateCachesForAttribute(const QualifiedName& attrName);

	void adoptTreeScope()
	{
	invalidateCaches();
	}

	void adoptDocument(Document& oldDocument, Document& newDocument)
	{
	if (&oldDocument == &newDocument) {
	invalidateCaches();
	return;
	}

	for (auto& cache : m_atomicNameCaches.values())
	cache->invalidateCacheForDocument(oldDocument);

	for (auto& list : m_tagCollectionNSCache.values()) {
	ASSERT(!list->isRootedAtDocument());
	list->invalidateCacheForDocument(oldDocument);
	}

	for (auto& collection : m_cachedCollections.values())
	collection->invalidateCacheForDocument(oldDocument);
	}

	private:
	std::pair<unsigned char, AtomicString> namedCollectionKey(CollectionType type, const AtomicString& name)
	{
	return std::pair<unsigned char, AtomicString>(type, name);
	}

	template <class NodeListType>
	std::pair<unsigned char, AtomicString> namedNodeListKey(const AtomicString& name)
	{
	return std::pair<unsigned char, AtomicString>(NodeListTypeIdentifier<NodeListType>::value(), name);
	}

	bool deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(Node&);

	// These two are currently mutually exclusive and could be unioned. Not very important as this class is large anyway.
	ChildNodeList* m_childNodeList;
	EmptyNodeList* m_emptyChildNodeList;

	NodeListAtomicNameCacheMap m_atomicNameCaches;
	TagCollectionNSCache m_tagCollectionNSCache;
	CollectionCacheMap m_cachedCollections;
	};

	class NodeMutationObserverData {
	WTF_MAKE_NONCOPYABLE(NodeMutationObserverData); WTF_MAKE_FAST_ALLOCATED;
	public:
	Vector<std::unique_ptr<MutationObserverRegistration>> registry;
	HashSet<MutationObserverRegistration*> transientRegistry;

	NodeMutationObserverData() { }
	};

	class NodeRareData : public NodeRareDataBase {
	WTF_MAKE_NONCOPYABLE(NodeRareData); WTF_MAKE_FAST_ALLOCATED;
	public:
	NodeRareData(RenderObject* renderer)
	: NodeRareDataBase(renderer)
	, m_connectedFrameCount(0)
	{ }

	void clearNodeLists() { m_nodeLists = nullptr; }
	NodeListsNodeData* nodeLists() const { return m_nodeLists.get(); }
	NodeListsNodeData& ensureNodeLists()
	{
	if (!m_nodeLists)
	m_nodeLists = std::make_unique<NodeListsNodeData>();
	return *m_nodeLists;
	}

	NodeMutationObserverData* mutationObserverData() { return m_mutationObserverData.get(); }
	NodeMutationObserverData& ensureMutationObserverData()
	{
	if (!m_mutationObserverData)
	m_mutationObserverData = std::make_unique<NodeMutationObserverData>();
	return *m_mutationObserverData;
	}

	unsigned connectedSubframeCount() const { return m_connectedFrameCount; }
	void incrementConnectedSubframeCount(unsigned amount)
	{
	m_connectedFrameCount += amount;
	}
	void decrementConnectedSubframeCount(unsigned amount)
	{
	ASSERT(m_connectedFrameCount);
	ASSERT(amount <= m_connectedFrameCount);
	m_connectedFrameCount -= amount;
	}

	private:
	unsigned m_connectedFrameCount : 10; // Must fit Page::maxNumberOfFrames.

	std::unique_ptr<NodeListsNodeData> m_nodeLists;
	std::unique_ptr<NodeMutationObserverData> m_mutationObserverData;
	};

	inline bool NodeListsNodeData::deleteThisAndUpdateNodeRareDataIfAboutToRemoveLastList(Node& ownerNode)
	{
	ASSERT(ownerNode.nodeLists() == this);
	if ((m_childNodeList ? 1 : 0) + (m_emptyChildNodeList ? 1 : 0) + m_atomicNameCaches.size()
	+ m_tagCollectionNSCache.size() + m_cachedCollections.size() != 1)
	return false;
	ownerNode.clearNodeLists();
	return true;
	}

	inline NodeRareData* Node::rareData() const
	{
	ASSERT_WITH_SECURITY_IMPLICATION(hasRareData());
	return static_cast<NodeRareData*>(m_data.m_rareData);
	}

	inline NodeRareData& Node::ensureRareData()
	{
	if (!hasRareData())
	materializeRareData();
	return *rareData();
	}

	// Ensure the 10 bits reserved for the m_connectedFrameCount cannot overflow
	static_assert(Page::maxNumberOfFrames < 1024, "Frame limit should fit in rare data count");

	} // namespace WebCore