Activate LayerImpl tree with sync+push instead of pointer swap

cc/picture_layer_tiling_set.h

Index: cc/picture_layer_tiling_set.h
diff --git a/cc/picture_layer_tiling_set.h b/cc/picture_layer_tiling_set.h
index 1c8467b18c8e4cce0154a828003ff911762730cd..a962290c75dd284546192dbf741880e4b06244f3 100644
--- a/cc/picture_layer_tiling_set.h
+++ b/cc/picture_layer_tiling_set.h
@@ -14,9 +14,11 @@ namespace cc {
 
 class CC_EXPORT PictureLayerTilingSet {
  public:
-  PictureLayerTilingSet(PictureLayerTilingClient* client);
+  explicit PictureLayerTilingSet(PictureLayerTilingClient* client);
   ~PictureLayerTilingSet();
 
+  void SetClient(PictureLayerTilingClient* client);
+
   // Shallow copies all data (except client and bounds from other).
   void CloneAll(
      const PictureLayerTilingSet& other,
@@ -104,7 +106,6 @@ class CC_EXPORT PictureLayerTilingSet {
   PictureLayerTilingClient* client_;
   gfx::Size layer_bounds_;
   ScopedPtrVector<PictureLayerTiling> tilings_;
-  Region invalidation_;
 
   friend class Iterator;
 };