Allow layers that need squashing to draw into the squashing layer in some cases.

Source/core/rendering/compositing/CompositingLayerAssigner.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google 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
@@ skipping 112 matching lines @@
     if (layer->renderer()->isVideo())
         return false;
 
     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;
+    if (layer->renderer()->clippingContainer() != squashingLayer.renderer()->clippingContainer()) {
+        if (!squashingLayer.compositedLayerMapping()->containingSquashedLayer(layer->renderer()->clippingContainer()))
+            return false;
+    }
 
     // Composited descendants need to be clipped by a child contianment graphics layer, which would not be available if the layer is
     if (m_compositor->clipsCompositingDescendants(layer))
         return false;
 
     if (layer->scrollsWithRespectTo(&squashingLayer))
         return false;
 
     const RenderLayer::AncestorDependentProperties& ancestorDependentProperties = layer->ancestorDependentProperties();
     const RenderLayer::AncestorDependentProperties& squashingLayerAncestorDependentProperties = squashingLayer.ancestorDependentProperties();
@@ skipping 126 matching lines @@
             squashingState.updateSquashingStateForNewMapping(layer->compositedLayerMapping(), layer->hasCompositedLayerMapping(), offsetFromTransformedAncestorForSquashingCLM);
         }
     }
 
     RenderLayerStackingNodeIterator iterator(*layer->stackingNode(), NormalFlowChildren | PositiveZOrderChildren);
     while (RenderLayerStackingNode* curNode = iterator.next())
         assignLayersToBackingsInternal(curNode->layer(), squashingState, layersChanged);
 }
 
 }