[#5] Pass gfx structs by const ref (gfx::Vector2dF)

cc/input/top_controls_manager.h

 // 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.
 
 #ifndef CC_INPUT_TOP_CONTROLS_MANAGER_H_
 #define CC_INPUT_TOP_CONTROLS_MANAGER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "cc/input/top_controls_state.h"
@@ skipping 35 matching lines @@
   KeyframedFloatAnimationCurve* animation() {
     return top_controls_animation_.get();
   }
   AnimationDirection animation_direction() { return animation_direction_; }
 
   void UpdateTopControlsState(TopControlsState constraints,
                               TopControlsState current,
                               bool animate);
 
   void ScrollBegin();
-  gfx::Vector2dF ScrollBy(const gfx::Vector2dF pending_delta);
+  gfx::Vector2dF ScrollBy(const gfx::Vector2dF& pending_delta);
   void ScrollEnd();
 
   // The caller should ensure that |Pinch{Begin,End}| are called within
   // the scope of |Scroll{Begin,End}|.
   void PinchBegin();
   void PinchEnd();
 
   gfx::Vector2dF Animate(base::TimeTicks monotonic_time);
 
  protected:
@@ skipping 30 matching lines @@
   float top_controls_hide_height_;
 
   bool pinch_gesture_active_;
 
   DISALLOW_COPY_AND_ASSIGN(TopControlsManager);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_TOP_CONTROLS_MANAGER_H_