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

cc/resources/image_layer_updater.h

Index: cc/resources/image_layer_updater.h
diff --git a/cc/resources/image_layer_updater.h b/cc/resources/image_layer_updater.h
index 1b92a6f1926593b9ec253623326b8c1fba63a5a7..b2235b180312d88960e00b9f08b27f7ddf8adb25 100644
--- a/cc/resources/image_layer_updater.h
+++ b/cc/resources/image_layer_updater.h
@@ -23,7 +23,7 @@ class CC_EXPORT ImageLayerUpdater : public LayerUpdater {
 
     virtual void Update(ResourceUpdateQueue* queue,
                         const gfx::Rect& source_rect,
-                        gfx::Vector2d dest_offset,
+                        const gfx::Vector2d& dest_offset,
                         bool partial_update) OVERRIDE;
 
    private:
@@ -40,7 +40,7 @@ class CC_EXPORT ImageLayerUpdater : public LayerUpdater {
   void UpdateTexture(ResourceUpdateQueue* queue,
                      PrioritizedResource* texture,
                      const gfx::Rect& source_rect,
-                     gfx::Vector2d dest_offset,
+                     const gfx::Vector2d& dest_offset,
                      bool partial_update);
 
   void SetBitmap(const SkBitmap& bitmap);