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

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 75f02ec95dd898d04f68dca62d69e40a23a88802..a939370cf1b4bb8283f3df0c1db31b69285822ba 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -368,12 +368,12 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
       LayerScrollOffsetDelegate* scroll_offset_delegate);
   bool IsExternalFlingActive() const;
 
-  void SetScrollOffset(gfx::Vector2d scroll_offset);
-  void SetScrollOffsetAndDelta(gfx::Vector2d scroll_offset,
+  void SetScrollOffset(const gfx::Vector2d& scroll_offset);
+  void SetScrollOffsetAndDelta(const gfx::Vector2d& scroll_offset,
                                const gfx::Vector2dF& scroll_delta);
   gfx::Vector2d scroll_offset() const { return scroll_offset_; }
 
-  void SetMaxScrollOffset(gfx::Vector2d max_scroll_offset);
+  void SetMaxScrollOffset(const gfx::Vector2d& max_scroll_offset);
   gfx::Vector2d max_scroll_offset() const { return max_scroll_offset_; }
 
   void SetScrollDelta(const gfx::Vector2dF& scroll_delta);
@@ -381,7 +381,7 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
 
   gfx::Vector2dF TotalScrollOffset() const;
 
-  void SetSentScrollDelta(gfx::Vector2d sent_scroll_delta);
+  void SetSentScrollDelta(const gfx::Vector2d& sent_scroll_delta);
   gfx::Vector2d sent_scroll_delta() const { return sent_scroll_delta_; }
 
   // Returns the delta of the scroll that was outside of the bounds of the