cc: Avoid expensive RenderingStats collection.

cc/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_PICTURE_PILE_H_
 #define CC_PICTURE_PILE_H_
 
 #include "cc/picture_pile_base.h"
 #include "ui/gfx/rect.h"
 
 namespace cc {
 class PicturePileImpl;
 class Region;
 struct RenderingStats;
 
 class CC_EXPORT PicturePile : public PicturePileBase {
  public:
   PicturePile();
 
   // Re-record parts of the picture that are invalid.
   // Invalidations are in layer space.
   void Update(
       ContentLayerClient* painter,
       const Region& invalidation,
       gfx::Rect visible_layer_rect,
-      RenderingStats& stats);
+      RenderingStats* stats);
 
   // Update other with a shallow copy of this (main => compositor thread commit)
   void PushPropertiesTo(PicturePileImpl* other);
 
  private:
   virtual ~PicturePile();
   friend class PicturePileImpl;
 
   // Add an invalidation to this picture list.  If the list needs to be
   // entirely recreated, leave it empty.  Do not call this on an empty list.
   void InvalidateRect(
       PictureList& picture_list,
       gfx::Rect invalidation);
 
   DISALLOW_COPY_AND_ASSIGN(PicturePile);
 };
 
 }  // namespace cc
 
 #endif  // CC_PICTURE_PILE_H_