Don't squash layers that have a clip or overflow clip.

Source/core/rendering/compositing/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 692 matching lines @@
     if (squashingWouldExceedSparsityTolerance(layer, squashingState))
         return false;
 
     // FIXME: this is not efficient, since it walks up the tree . We should store these values on the AncestorDependentPropertiesCache.
     ASSERT(squashingState.hasMostRecentMapping);
     const RenderLayer& squashingLayer = squashingState.mostRecentMapping->owningLayer();
 
     if (layer->renderer()->clippingContainer() != squashingLayer.renderer()->clippingContainer())
         return false;
 
+    // FIXME: this seems to be overly aggressive. clipsCompositingDescendants() should suffice. However, it does not fix all testcases,
+    // in particular crbug.com/366101.
+    if (layer->renderer()->hasClipOrOverflowClip())
+        return false;
+
     if (layer->scrollsWithRespectTo(&squashingLayer))
         return false;
 
     const RenderLayer::AncestorDependentProperties& ancestorDependentProperties = layer->ancestorDependentProperties();
     const RenderLayer::AncestorDependentProperties& squashingLayerAncestorDependentProperties = squashingLayer.ancestorDependentProperties();
 
     if (ancestorDependentProperties.opacityAncestor != squashingLayerAncestorDependentProperties.opacityAncestor)
         return false;
 
     if (ancestorDependentProperties.transformAncestor != squashingLayerAncestorDependentProperties.transformAncestor)
@@ skipping 989 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore