cc: Don't pass simple well-defined classes by reference.

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 83a2ffaf53ec05229093559f6d3bda601c160026..19aa727ffe3e38d3bb6b09223fb3ab936ad6801a 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -163,10 +163,10 @@ class CC_EXPORT LayerImpl : LayerAnimationValueObserver {
     return is_container_for_fixed_position_layers_;
   }
 
-  void SetFixedContainerSizeDelta(const gfx::Vector2dF& delta) {
+  void SetFixedContainerSizeDelta(gfx::Vector2dF delta) {
     fixed_container_size_delta_ = delta;
   }
-  const gfx::Vector2dF& fixed_container_size_delta() const {
+  gfx::Vector2dF fixed_container_size_delta() const {
     return fixed_container_size_delta_;
   }