Set root clip layer not to maskToBounds.

public/platform/WebLayerTreeView.h

 /*
  * Copyright (C) 2011 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 105 matching lines @@
 
     // Prevents updates to layer tree from becoming visible.
     virtual void setDeferCommits(bool deferCommits) { }
 
     // Take responsiblity for this layer's animations, even if this layer hasn't yet
     // been added to the tree.
     virtual void registerForAnimations(WebLayer* layer) { }
 
     // Identify key layers to the compositor when using the pinch virtual viewport.
     virtual void registerPinchViewportLayers(
-        const WebLayer* innerViewportClipLayer,
+        const WebLayer* innerViewportContainerLayer,
         const WebLayer* pageScaleLayerLayer,
         const WebLayer* innerViewportScrollLayer,
         const WebLayer* outerViewportScrollLayer,
         const WebLayer* innerViewportHorizontalScrollbarLayer,
         const WebLayer* innerViewportVerticalScrollbarLayer) { }
     virtual void clearPinchViewportLayers() { }
 
     // Debugging / dangerous ---------------------------------------------
 
     // Toggles the FPS counter in the HUD layer
     virtual void setShowFPSCounter(bool) { }
 
     // Toggles the paint rects in the HUD layer
     virtual void setShowPaintRects(bool) { }
 
     // Toggles the debug borders on layers
     virtual void setShowDebugBorders(bool) { }
 
     // Toggles continuous painting
     virtual void setContinuousPaintingEnabled(bool) { }
 
     // Toggles scroll bottleneck rects on the HUD layer
     virtual void setShowScrollBottleneckRects(bool) { }
 };
 
 } // namespace WebKit
 
 #endif // WebLayerTreeView_h