compositor-worker: blink->cc plumbing

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 485688c0a4d5ad7e348d6a30a07df318e525efaf..e6e3a072f3dc04709a67fef3d987f989c34f0ec0 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -1115,6 +1115,10 @@ void LayerTreeHost::RecordFrameTimingEvents(
                                    std::move(main_frame_events));
 }
 
+void LayerTreeHost::SetLayerTreeMutator(LayerTreeMutator* mutator) {
+  proxy_->SetMutator(mutator);
+}
+
 Layer* LayerTreeHost::LayerById(int id) const {
   LayerIdMap::const_iterator iter = layer_id_map_.find(id);
   return iter != layer_id_map_.end() ? iter->second : NULL;