compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

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 fee2d6c61e4f92a745574b96d3008c01245076af..8e7fcc255af6d9e69cd181121c556e6970a1248e 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -1265,6 +1265,11 @@ void LayerTreeHost::SetAuthoritativeVSyncInterval(
   proxy_->SetAuthoritativeVSyncInterval(interval);
 }
 
+void LayerTreeHost::SetLayerTreeMutator(
+    std::unique_ptr<LayerTreeMutator> mutator) {
+  proxy_->SetMutator(std::move(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;