[#6]Pass gfx structs by const ref (gfx::Vector2d)

cc/output/software_output_device.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_OUTPUT_SOFTWARE_OUTPUT_DEVICE_H_
 #define CC_OUTPUT_SOFTWARE_OUTPUT_DEVICE_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
@@ skipping 37 matching lines @@
   // SkCanvas instance returned by |BeginPaint| and should discard any reference
   // that it holds to it.
   virtual void EndPaint(SoftwareFrameData* frame_data);
 
   // Copies pixels inside |rect| from the current software framebuffer to
   // |output|. Fails if there is no current softwareframebuffer.
   virtual void CopyToBitmap(const gfx::Rect& rect, SkBitmap* output);
 
   // Blit the pixel content of the SoftwareOutputDevice by |delta| with the
   // write clipped to |clip_rect|.
-  virtual void Scroll(gfx::Vector2d delta,
-                      const gfx::Rect& clip_rect);
+  virtual void Scroll(const gfx::Vector2d& delta, const gfx::Rect& clip_rect);
 
   // Discard the backing buffer in the surface provided by this instance.
   virtual void DiscardBackbuffer() {}
 
   // Ensures that there is a backing buffer available on this instance.
   virtual void EnsureBackbuffer() {}
 
   // TODO(skaslev) Remove this after UberCompositor lands.
   // Called in response to receiving a SwapBuffersAck. At this point, software
   // frame identified by id can be reused or discarded as it is no longer being
@@ skipping 11 matching lines @@
   skia::RefPtr<SkCanvas> canvas_;
   scoped_ptr<gfx::VSyncProvider> vsync_provider_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SoftwareOutputDevice);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_SOFTWARE_OUTPUT_DEVICE_H_