Go to: http://scarey.org/albums/lp and try to click on the album art to make it flip.
The back cover flashes, then disappears. The front cover remains visible, rendered backward.
When applying the transform to flip, we're not doing layout so not updating the "m_hasTransformedAncestor" flags.
Forcing layout when style changes between having a transform and not having one is not enough to fix this; we evaluate compositing at the start of the transition, when we've set the identity matrix on an ancestor (which will then animate to a 3D matrix).
Also have to deal with animations that go from 2D -> 3D matrix.
Created attachment 236148 [details]
Attachment 236148 [details] did not pass style-queue:
ERROR: Source/WebCore/rendering/RenderLayerCompositor.cpp:2395: Multi line control clauses should use braces. [whitespace/braces] 
Total errors found: 1 in 5 files
If any of these errors are false positives, please file a bug against check-webkit-style.