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

cc/test/layer_tree_test.cc

 // Copyright 2011 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/test/layer_tree_test.h"
 
 #include "base/command_line.h"
 #include "cc/animation/animation.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/layer_animation_controller.h"
@@ skipping 208 matching lines @@
     test_hooks_->DidBeginMainFrame();
   }
 
   virtual void Animate(double monotonic_time) OVERRIDE {
     test_hooks_->Animate(base::TimeTicks::FromInternalValue(
         monotonic_time * base::Time::kMicrosecondsPerSecond));
   }
 
   virtual void Layout() OVERRIDE { test_hooks_->Layout(); }
 
-  virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+  virtual void ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                    float scale) OVERRIDE {
     test_hooks_->ApplyScrollAndScale(scroll_delta, scale);
   }
 
   virtual scoped_ptr<OutputSurface> CreateOutputSurface(bool fallback)
       OVERRIDE {
     return test_hooks_->CreateOutputSurface(fallback);
   }
 
   virtual void DidInitializeOutputSurface(bool succeeded) OVERRIDE {
@@ skipping 466 matching lines @@
     const {
   if (impl->pending_tree())
     return impl->pending_tree()->source_frame_number();
   if (impl->active_tree())
     return impl->active_tree()->source_frame_number();
   // Source frames start at 0, so this is invalid.
   return -1;
 }
 
 }  // namespace cc