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

cc/trees/layer_tree_host_impl.h

 // 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.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 111 matching lines @@
   virtual void OnRootLayerDelegatedScrollOffsetChanged() OVERRIDE;
   virtual void ScrollEnd() OVERRIDE;
   virtual InputHandler::ScrollStatus FlingScrollBegin() OVERRIDE;
   virtual void NotifyCurrentFlingVelocity(
       const gfx::Vector2dF& velocity) OVERRIDE;
   virtual void MouseMoveAt(gfx::Point viewport_point) OVERRIDE;
   virtual void PinchGestureBegin() OVERRIDE;
   virtual void PinchGestureUpdate(float magnify_delta,
                                   gfx::Point anchor) OVERRIDE;
   virtual void PinchGestureEnd() OVERRIDE;
-  virtual void StartPageScaleAnimation(gfx::Vector2d target_offset,
+  virtual void StartPageScaleAnimation(const gfx::Vector2d& target_offset,
                                        bool anchor_point,
                                        float page_scale,
                                        base::TimeDelta duration) OVERRIDE;
   virtual void ScheduleAnimation() OVERRIDE;
   virtual bool HaveTouchEventHandlersAt(gfx::Point viewport_port) OVERRIDE;
   virtual scoped_ptr<SwapPromiseMonitor> CreateLatencyInfoSwapPromiseMonitor(
       ui::LatencyInfo* latency) OVERRIDE;
 
   // TopControlsManagerClient implementation.
   virtual void DidChangeTopControlsPosition() OVERRIDE;
@@ skipping 509 matching lines @@
   int id_;
 
   std::set<SwapPromiseMonitor*> swap_promise_monitor_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_