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

cc/layers/layer_impl.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_LAYERS_LAYER_IMPL_H_
 #define CC_LAYERS_LAYER_IMPL_H_
 
 #include <set>
 #include <string>
 
@@ skipping 344 matching lines @@
                                       float page_scale_factor,
                                       bool animating_transform_to_screen,
                                       float* contents_scale_x,
                                       float* contents_scale_y,
                                       gfx::Size* content_bounds);
 
   void SetScrollOffsetDelegate(
       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_; }
 
   gfx::Vector2d MaxScrollOffset() const;
   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
   // initial scroll
   gfx::Vector2dF ScrollBy(const gfx::Vector2dF& scroll);
 
   void SetScrollClipLayer(int scroll_clip_layer_id);
   bool scrollable() const { return !!scroll_clip_layer_; }
 
   void set_user_scrollable_horizontal(bool scrollable) {
@@ skipping 273 matching lines @@
   DrawProperties<LayerImpl> draw_properties_;
 
   scoped_refptr<base::debug::ConvertableToTraceFormat> debug_info_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_IMPL_H_