cc: Add PictureLayerTiling for impl-side painting

cc/picture_layer.cc

Index: cc/picture_layer.cc
diff --git a/cc/picture_layer.cc b/cc/picture_layer.cc
index d1f6c3d06be7e6bf973f72179c8cd33b1fae7e4a..01eb454b4d8ab0ce67b9c60486ebcee3eb14ea7d 100644
--- a/cc/picture_layer.cc
+++ b/cc/picture_layer.cc
@@ -31,6 +31,7 @@ void PictureLayer::pushPropertiesTo(LayerImpl* base_layer) {
   PictureLayerImpl* layer_impl = static_cast<PictureLayerImpl*>(base_layer);
   pile_.PushPropertiesTo(layer_impl->pile_);
 
+  // TODO(enne): Need to sync tiling from active tree prior to this?
   // TODO(nduca): Need to invalidate tiles here from pile's invalidation info.
 }