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

cc/input/input_handler.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_INPUT_INPUT_HANDLER_H_
 #define CC_INPUT_INPUT_HANDLER_H_
 
 #include "base/basictypes.h"
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
@@ skipping 99 matching lines @@
   // LayerScrollOffsetDelegate.GetTotalScrollOffset has changed for reasons
   // other than a SetTotalScrollOffset call.
   // NOTE: This should only called after a valid delegate was set via a call to
   // SetRootLayerScrollOffsetDelegate.
   virtual void OnRootLayerDelegatedScrollOffsetChanged() = 0;
 
   virtual void PinchGestureBegin() = 0;
   virtual void PinchGestureUpdate(float magnify_delta, gfx::Point anchor) = 0;
   virtual void PinchGestureEnd() = 0;
 
-  virtual void StartPageScaleAnimation(gfx::Vector2d target_offset,
+  virtual void StartPageScaleAnimation(const gfx::Vector2d& target_offset,
                                        bool anchor_point,
                                        float page_scale,
                                        base::TimeDelta duration) = 0;
 
   // Request another callback to InputHandlerClient::Animate().
   virtual void ScheduleAnimation() = 0;
 
   virtual bool HaveTouchEventHandlersAt(gfx::Point viewport_point) = 0;
 
   // Calling CreateLatencyInfoSwapPromiseMonitor() to get a scoped
   // LatencyInfoSwapPromiseMonitor. During the life time of the
   // LatencyInfoSwapPromiseMonitor, if SetNeedsRedraw() or SetNeedsRedrawRect()
   // is called on LayerTreeHostImpl, the original latency info will be turned
   // into a LatencyInfoSwapPromise.
   virtual scoped_ptr<SwapPromiseMonitor> CreateLatencyInfoSwapPromiseMonitor(
       ui::LatencyInfo* latency) = 0;
 
  protected:
   InputHandler() {}
   virtual ~InputHandler() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InputHandler);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_INPUT_HANDLER_H_