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

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 <map>
 #include <set>
 #include <string>
@@ skipping 148 matching lines @@
     SetNeedsPushProperties();
   }
   void set_opacity_tree_index(int index) {
     opacity_tree_index_ = index;
     SetNeedsPushProperties();
   }
   int clip_tree_index() const { return clip_tree_index_; }
   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();
   }
   gfx::Vector2dF offset_to_transform_parent() const {
     return offset_to_transform_parent_;
   }
 
   const gfx::Rect& visible_rect_from_property_trees() const {
     return visible_rect_from_property_trees_;
   }
@@ skipping 649 matching lines @@
 
   std::vector<FrameTimingRequest> frame_timing_requests_;
   bool frame_timing_requests_dirty_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_IMPL_H_