Only draw the overhang pattern on overhang areas.

cc/trees/layer_tree_impl.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <list>
 #include <string>
 #include <vector>
@@ skipping 157 matching lines @@
 
   void set_ui_resource_request_queue(const UIResourceRequestQueue& queue);
 
   const LayerImplList& RenderSurfaceLayerList() const;
 
   // These return the size of the root scrollable area and the size of
   // the user-visible scrolling viewport, in CSS layout coordinates.
   gfx::Size ScrollableSize() const;
   gfx::SizeF ScrollableViewportSize() const;
 
+  gfx::Rect RootScrollLayerDeviceViewportBounds() const;
+
   LayerImpl* LayerById(int id);
 
   // These should be called by LayerImpl's ctor/dtor.
   void RegisterLayer(LayerImpl* layer);
   void UnregisterLayer(LayerImpl* layer);
 
   AnimationRegistrar* animationRegistrar() const;
 
   void PushPersistedState(LayerTreeImpl* pending_tree);
 
@@ skipping 83 matching lines @@
 
   UIResourceRequestQueue ui_resource_request_queue_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_