[#2] Pass gfx structs by const ref (gfx::Rect, gfx::RectF)

cc/resources/picture_pile.h

 // Copyright 2012 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_RESOURCES_PICTURE_PILE_H_
 #define CC_RESOURCES_PICTURE_PILE_H_
 
 #include "cc/resources/picture_pile_base.h"
 #include "ui/gfx/rect.h"
 
 namespace cc {
 class PicturePileImpl;
 class Region;
 class RenderingStatsInstrumentation;
 
 class CC_EXPORT PicturePile : public PicturePileBase {
  public:
   PicturePile();
 
   // Re-record parts of the picture that are invalid.
   // Invalidations are in layer space.
   // Return true iff the pile was modified.
   bool Update(
       ContentLayerClient* painter,
       SkColor background_color,
       bool contents_opaque,
       const Region& invalidation,
-      gfx::Rect visible_layer_rect,
+      const gfx::Rect& visible_layer_rect,
       int frame_number,
       RenderingStatsInstrumentation* stats_instrumentation);
 
   void set_num_raster_threads(int num_raster_threads) {
     num_raster_threads_ = num_raster_threads;
   }
 
   void set_slow_down_raster_scale_factor(int factor) {
     slow_down_raster_scale_factor_for_debug_ = factor;
   }
 
   void set_show_debug_picture_borders(bool show) {
     show_debug_picture_borders_ = show;
   }
 
  protected:
   virtual ~PicturePile();
 
  private:
   friend class PicturePileImpl;
 
   DISALLOW_COPY_AND_ASSIGN(PicturePile);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_PICTURE_PILE_H_