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

cc/layers/layer.h

 // Copyright 2010 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_H_
 #define CC_LAYERS_LAYER_H_
 
 #include <set>
 #include <string>
 
@@ skipping 249 matching lines @@
   }
   RenderSurface* render_surface() const {
     return draw_properties_.render_surface.get();
   }
   int num_unclipped_descendants() const {
     return draw_properties_.num_unclipped_descendants;
   }
 
   void SetScrollOffset(gfx::Vector2d scroll_offset);
   gfx::Vector2d scroll_offset() const { return scroll_offset_; }
-  void SetScrollOffsetFromImplSide(gfx::Vector2d scroll_offset);
+  void SetScrollOffsetFromImplSide(const gfx::Vector2d& scroll_offset);
 
   gfx::Vector2d MaxScrollOffset() const;
-
   void SetScrollClipLayerId(int clip_layer_id);
   bool scrollable() const { return scroll_clip_layer_id_ != INVALID_ID; }
 
   void SetUserScrollable(bool horizontal, bool vertical);
   bool user_scrollable_horizontal() const {
     return user_scrollable_horizontal_;
   }
   bool user_scrollable_vertical() const { return user_scrollable_vertical_; }
 
   void SetShouldScrollOnMainThread(bool should_scroll_on_main_thread);
@@ skipping 335 matching lines @@
   DrawProperties<Layer> draw_properties_;
 
   PaintProperties paint_properties_;
 
   DISALLOW_COPY_AND_ASSIGN(Layer);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_H_