Update scroll parent correctly for squashing layers.

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 02d27c174078b8931bc396cccfbad8239a448ef6..a16015efcad60bfa42af6fd6050c46843eaa8033 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -193,6 +193,9 @@ RenderLayerCompositor* RenderLayer::compositor() const
 
 void RenderLayer::contentChanged(ContentChangeType changeType)
 {
+    // updateLayerCompositingState will query compositingReasons for accelerated overflow scrolling.

[ojan, 2014/03/12 18:30:25]

Is there a test that hits this? It's useful to list the test in the comment so
that the person who tries to fix this can easily tell if this still reproduces.

[Ian Vollick, 2014/03/12 20:03:32]

Added a test for this.

+    DisableCompositingQueryAsserts disabler;

[abarth-chromium, 2014/03/12 18:45:40]

It's too bad that we're regressing this chicken-egg issue.  We recently removed
the assert disabler from this function.

[Ian Vollick, 2014/03/12 20:03:32]

Not a regression, just a gap in coverage. We were always asserting here, we just
didn't know it.

+
     // This can get called when video becomes accelerated, so the layers may change.
     if (changeType == CanvasChanged || changeType == VideoChanged || changeType == FullScreenChanged)
         compositor()->updateLayerCompositingState(this);