Update scroll parent correctly for squashing layers.

Source/core/rendering/RenderLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 175 matching lines @@
 
 RenderLayerCompositor* RenderLayer::compositor() const
 {
     if (!renderer()->view())
         return 0;
     return renderer()->view()->compositor();
 }
 
 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);
 
     if (changeType == CanvasContextChanged)
         compositor()->setNeedsCompositingUpdate(CompositingUpdateAfterCanvasContextChange);
 
     if (m_compositedLayerMapping)
         m_compositedLayerMapping->contentChanged(changeType);
 }
@@ skipping 3864 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif