cc: Merge the DrawLayer()/DrawFrame() and SwapBuffers() methods.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index ad77b50daeeaf2d3872f30627b77a81036e1250a..da82bc25c8660304b46a784214f25ff831859d80 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -309,7 +309,7 @@ class CC_EXPORT LayerTreeHostImpl
   // DidDrawAllLayers must also be called, regardless of whether DrawLayers is
   // called between the two.
   virtual DrawResult PrepareToDraw(FrameData* frame);
-  void DrawLayers(FrameData* frame);
+  virtual bool DrawLayers(FrameData* frame);
   // Must be called if and only if PrepareToDraw was called.
   void DidDrawAllLayers(const FrameData& frame);
 
@@ -420,7 +420,6 @@ class CC_EXPORT LayerTreeHostImpl
     return image_decode_controller_.get();
   }
 
-  virtual bool SwapBuffers(const FrameData& frame);
   virtual void WillBeginImplFrame(const BeginFrameArgs& args);
   virtual void DidFinishImplFrame();
   void DidModifyTilePriorities();