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

cc/resources/layer_updater.h

Index: cc/resources/layer_updater.h
diff --git a/cc/resources/layer_updater.h b/cc/resources/layer_updater.h
index d12d7b4b35e577a39844911c8ca339f2efef4462..44c6765f1ed62c7049315c2c63efc1402edb2596 100644
--- a/cc/resources/layer_updater.h
+++ b/cc/resources/layer_updater.h
@@ -30,8 +30,9 @@ class CC_EXPORT LayerUpdater : public base::RefCounted<LayerUpdater> {
     // instead of an argument passed to Update().
     virtual void Update(ResourceUpdateQueue* queue,
                         const gfx::Rect& source_rect,
-                        gfx::Vector2d dest_offset,
+                        const gfx::Vector2d& dest_offset,
                         bool partial_update) = 0;
+
    protected:
     explicit Resource(scoped_ptr<PrioritizedResource> texture);