Disable clipping on root scroller's ancestors.

third_party/WebKit/Source/platform/graphics/GraphicsLayer.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Intel Corporation. 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 306 matching lines @@
 
     Color m_backgroundColor;
     float m_opacity;
 
     WebBlendMode m_blendMode;
 
     bool m_hasTransformOrigin : 1;
     bool m_contentsOpaque : 1;
     bool m_shouldFlattenTransform: 1;
     bool m_backfaceVisibility : 1;
-    bool m_masksToBounds : 1;
     bool m_drawsContent : 1;
     bool m_contentsVisible : 1;
     bool m_isRootForIsolatedGroup : 1;
 
     bool m_hasScrollParent : 1;
     bool m_hasClipParent : 1;
 
     bool m_painted : 1;
 
     bool m_isTrackingPaintInvalidations : 1;
@@ skipping 39 matching lines @@
 };
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the blink namespace for ease of invocation from gdb.
 void PLATFORM_EXPORT showGraphicsLayerTree(const blink::GraphicsLayer*);
 #endif
 
 #endif // GraphicsLayer_h