Created attachment 62909 [details]
Load the attached testcase in Safari, switch to another tab, then switch back. You often hit:
SHOULD NEVER BE REACHED
(RenderLayerBacking.cpp:941 void WebCore::RenderLayerBacking::paintIntoLayer(WebCore::RenderLayer*, WebCore::GraphicsContext*, const WebCore::IntRect&, WebCore::PaintBehavior, WebCore::GraphicsLayerPaintingPhase, WebCore::RenderObject*))
The issue here is that as the root layer attachment changes, setDrawsContent(true) gets called on the RenderView's compositing layer, which in turn cause a -setNeedsDisplay. That should never happen.
Created attachment 62970 [details]
Comment on attachment 62970 [details]
Can you land a manual test? Just an HTML file with steps to reproduce in it. We do have a directory full of manual tests, although I’m not sure we get maximum value from them.
http://trac.webkit.org/changeset/64296, including manual test.