tree b43f5e0ccd890dd995d54785c219acc0c85860ef
parent c7ff48c76bf3f473e426438ee8342c683387f691
author simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1571339181 +0000
committer simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1571339181 +0000

[iOS Sim] Layout Test scrollingcoordinator/ios/ui-scroll-fixed.html is a flaky failure
https://bugs.webkit.org/show_bug.cgi?id=196612
rdar://problem/49612867

Reviewed by Antti Koivisto.

This test hit a really obscure bug where a combination of an immediate scroll, and
an ancestor reposition left the layer position of a position:fixed layer unchanged.
The position of this layer in the UI process had been previously modified by
the scrolling tree for the scroll, but because the WebContent-side mutations left
the actual position unchanged, we'd never apply a new position via a commit, so left
the layer in the wrong location.

Removing the m_wasScrolledByDelegatedScrollingSincePreviousCommit check in ScrollingTree::applyLayerPositionsAfterCommit()
fixes this, but has perf implications. Alternative fixes require complex state tracking.
Since this is so hard to hit with noisy user scrolling, just change the test to avoid
the perfect storm of scrolls and offsets.

* platform/ios-simulator-wk2/TestExpectations:
* scrollingcoordinator/ios/ui-scroll-fixed-expected.html:
* scrollingcoordinator/ios/ui-scroll-fixed.html:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@251251 268f45cc-cd09-0410-ab3c-d52691b4dbfc