Activate LayerImpl tree with sync+push instead of pointer swap

cc/picture_layer_impl.h

Index: cc/picture_layer_impl.h
diff --git a/cc/picture_layer_impl.h b/cc/picture_layer_impl.h
index 5e3184be94785734caf115dbae58f6f4181c564f..cb1861c2b4f901de44562d73cbc93baf62f76268 100644
--- a/cc/picture_layer_impl.h
+++ b/cc/picture_layer_impl.h
@@ -29,6 +29,9 @@ public:
 
   // LayerImpl overrides.
   virtual const char* layerTypeAsString() const OVERRIDE;
+  virtual scoped_ptr<LayerImpl> createLayerImpl(
+      LayerTreeImpl* treeImpl) OVERRIDE;
+  virtual void pushPropertiesTo(LayerImpl* layer) OVERRIDE;
   virtual void appendQuads(QuadSink&, AppendQuadsData&) OVERRIDE;
   virtual void dumpLayerProperties(std::string*, int indent) const OVERRIDE;
   virtual void didUpdateTransforms() OVERRIDE;
@@ -63,7 +66,7 @@ protected:
   void ManageTilings(float ideal_contents_scale);
   void CleanUpUnusedTilings(std::vector<PictureLayerTiling*> used_tilings);
 
-  PictureLayerTilingSet tilings_;
+  scoped_ptr<PictureLayerTilingSet> tilings_;
   scoped_refptr<PicturePileImpl> pile_;
   Region invalidation_;