cc: Add some more infrastructure for two trees

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 2d592d342e5dba1b6378bdb06ae0341ea3cc3fcf..5614f0ce20d279f4cf782646e07aab04a5772564 100644
--- a/cc/picture_layer_impl.h
+++ b/cc/picture_layer_impl.h
@@ -39,12 +39,15 @@ public:
 
   // PushPropertiesTo active tree => pending tree
   void SyncFromActiveLayer(const PictureLayerImpl* other);
+  void SyncTilingFromActiveLayer(const PictureLayerTiling* tiling);
 
 protected:
   PictureLayerImpl(LayerTreeImpl* treeImpl, int id);
+  void AddTiling(float contents_scale, gfx::Size tile_size);
 
   PictureLayerTilingSet tilings_;
   scoped_refptr<PicturePileImpl> pile_;
+  Region invalidation_;
 
   gfx::Transform last_screen_space_transform_;
   double last_update_time_;