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

cc/animation/scroll_offset_animation_curve.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_ANIMATION_SCROLL_OFFSET_ANIMATION_CURVE_H_
 #define CC_ANIMATION_SCROLL_OFFSET_ANIMATION_CURVE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/animation/animation_curve.h"
 #include "cc/base/cc_export.h"
 
 namespace cc {
 
 class TimingFunction;
 
 class CC_EXPORT ScrollOffsetAnimationCurve : public AnimationCurve {
  public:
   static scoped_ptr<ScrollOffsetAnimationCurve> Create(
-      gfx::Vector2dF target_value,
+      const gfx::Vector2dF& target_value,
       scoped_ptr<TimingFunction> timing_function);
 
   virtual ~ScrollOffsetAnimationCurve();
 
-  void SetInitialValue(gfx::Vector2dF initial_value);
+  void SetInitialValue(const gfx::Vector2dF& initial_value);
   gfx::Vector2dF GetValue(double t) const;
 
   // AnimationCurve implementation
   virtual double Duration() const OVERRIDE;
   virtual CurveType Type() const OVERRIDE;
   virtual scoped_ptr<AnimationCurve> Clone() const OVERRIDE;
 
  private:
-  ScrollOffsetAnimationCurve(gfx::Vector2dF target_value,
+  ScrollOffsetAnimationCurve(const gfx::Vector2dF& target_value,
                              scoped_ptr <TimingFunction> timing_function);
 
   gfx::Vector2dF initial_value_;
   gfx::Vector2dF target_value_;
   double duration_;
 
   scoped_ptr<TimingFunction> timing_function_;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollOffsetAnimationCurve);
 };
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_SCROLL_OFFSET_ANIMATION_CURVE_H_