Activate LayerImpl tree with sync+push instead of pointer swap

cc/picture_pile_impl.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_IMPL_H_
 #define CC_PICTURE_PILE_IMPL_H_
 
 #include <list>
 #include <map>
 
@@ skipping 20 matching lines @@
   // It's only safe to call paint on a cloned version.
   // It is assumed that contentsScale has already been applied to this canvas.
   void Raster(
       SkCanvas* canvas,
       gfx::Rect content_rect,
       float contents_scale,
       RenderingStats* stats);
 
   void GatherPixelRefs(const gfx::Rect&, std::list<skia::LazyPixelRef*>&);
 
+  void PushPropertiesTo(PicturePileImpl* other);
+
   skia::RefPtr<SkPicture> GetFlattenedPicture();
 
  private:
   friend class PicturePile;
 
   PicturePileImpl();
   ~PicturePileImpl();
 
   typedef std::map<base::PlatformThreadId, scoped_refptr<PicturePileImpl> >
       CloneMap;
   CloneMap clones_;
 
   DISALLOW_COPY_AND_ASSIGN(PicturePileImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_PICTURE_PILE_IMPL_H_