[#2] Pass gfx structs by const ref (gfx::Rect, gfx::RectF)

gpu/command_buffer/client/context_support.h

 // Copyright 2013 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 GPU_COMMAND_BUFFER_CLIENT_CONTEXT_SUPPORT_H_
 #define GPU_COMMAND_BUFFER_CLIENT_CONTEXT_SUPPORT_H_
 
 #include "base/callback.h"
 #include "ui/gfx/rect.h"
 
@@ skipping 10 matching lines @@
   // passed the glEndQueryEXT() point.
   virtual void SignalQuery(uint32 query, const base::Closure& callback) = 0;
 
   // For onscreen contexts, indicates that the surface visibility has changed.
   // Clients aren't expected to draw to an invisible surface.
   virtual void SetSurfaceVisible(bool visible) = 0;
 
   virtual void SendManagedMemoryStats(const ManagedMemoryStats& stats) = 0;
 
   virtual void Swap() = 0;
-  virtual void PartialSwapBuffers(gfx::Rect sub_buffer) = 0;
+  virtual void PartialSwapBuffers(const gfx::Rect& sub_buffer) = 0;
 
   virtual void SetSwapBuffersCompleteCallback(
       const base::Closure& callback) = 0;
 
  protected:
   ContextSupport() {}
   virtual ~ContextSupport() {}
 };
 
 }
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_CONTEXT_SUPPORT_H_