[#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 bb4358fd238b1f220cd94eac220c78e5c18e5deb..a901a6457a17f4dbff243c44c25c41131f506881 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -362,8 +362,8 @@ 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_; }
 
@@ -371,13 +371,12 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   gfx::Vector2dF ClampScrollToMaxScrollOffset();
   void SetScrollbarPosition(ScrollbarLayerImplBase* scrollbar_layer,
                             LayerImpl* scrollbar_clip_layer) const;
-
   void SetScrollDelta(const gfx::Vector2dF& scroll_delta);
   gfx::Vector2dF ScrollDelta() const;
 
   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