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

cc/layers/layer_impl.h

 // Copyright 2011 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_IMPL_H_
 #define CC_LAYERS_LAYER_IMPL_H_
 
 #include <string>
 
 #include "base/logging.h"
@@ skipping 145 matching lines @@
   gfx::PointF position() const { return position_; }
 
   void SetIsContainerForFixedPositionLayers(bool container) {
     is_container_for_fixed_position_layers_ = container;
   }
   // This is a non-trivial function in Layer.
   bool IsContainerForFixedPositionLayers() const {
     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_;
   }
 
   void SetPositionConstraint(const LayerPositionConstraint& constraint) {
     position_constraint_ = constraint;
   }
   const LayerPositionConstraint& position_constraint() const {
     return position_constraint_;
   }
 
@@ skipping 352 matching lines @@
   // Group of properties that need to be computed based on the layer tree
   // hierarchy before layers can be drawn.
   DrawProperties<LayerImpl, RenderSurfaceImpl> draw_properties_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_IMPL_H_