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 f41bc9fea43e116e44e5cb744e9d05c65199a90c..efd09287bf685211f78205a4e1e2dd82e5ea80c9 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -1268,6 +1268,11 @@ 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;