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

cc/output/software_output_device.cc

 // 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.
 
 #include "cc/output/software_output_device.h"
 
 #include "base/logging.h"
 #include "cc/output/software_frame_data.h"
 #include "third_party/skia/include/core/SkBitmapDevice.h"
 #include "third_party/skia/include/core/SkCanvas.h"
@@ skipping 30 matching lines @@
   frame_data->handle = base::SharedMemory::NULLHandle();
 }
 
 void SoftwareOutputDevice::CopyToBitmap(
     const gfx::Rect& rect, SkBitmap* output) {
   DCHECK(device_);
   const SkBitmap& bitmap = device_->accessBitmap(false);
   bitmap.extractSubset(output, gfx::RectToSkIRect(rect));
 }
 
-void SoftwareOutputDevice::Scroll(
-    gfx::Vector2d delta, const gfx::Rect& clip_rect) {
+void SoftwareOutputDevice::Scroll(const gfx::Vector2d& delta,
+                                  const gfx::Rect& clip_rect) {
   NOTIMPLEMENTED();
 }
 
 void SoftwareOutputDevice::ReclaimSoftwareFrame(unsigned id) {
   NOTIMPLEMENTED();
 }
 
 gfx::VSyncProvider* SoftwareOutputDevice::GetVSyncProvider() {
   return vsync_provider_.get();
 }
 
 }  // namespace cc