Pass gfx structs by const ref(gfx::Vector2D/F)

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 f3eb4cea90fca7de26b3025c93c5c09f2176ba04..6fc5cb296f9e10ce6269dd96c63decdcfb285fa2 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -166,7 +166,7 @@ class CC_EXPORT LayerImpl : public LayerAnimationValueObserver,
   int transform_tree_index() const { return transform_tree_index_; }
   int opacity_tree_index() const { return opacity_tree_index_; }
 
-  void set_offset_to_transform_parent(gfx::Vector2dF offset) {
+  void set_offset_to_transform_parent(const gfx::Vector2dF& offset) {
     offset_to_transform_parent_ = offset;
     SetNeedsPushProperties();
   }