WIP - compositor worker mega patch.

cc/trees/proxy_impl.cc

Index: cc/trees/proxy_impl.cc
diff --git a/cc/trees/proxy_impl.cc b/cc/trees/proxy_impl.cc
index 9a779ea00a6eccf0dbacd841d9cbca4ea3231877..ee0418fc0cd29ed47411100f7ce7a82d7c9db2b8 100644
--- a/cc/trees/proxy_impl.cc
+++ b/cc/trees/proxy_impl.cc
@@ -110,6 +110,12 @@ void ProxyImpl::SetThrottleFrameProductionOnImpl(bool throttle) {
   scheduler_->SetThrottleFrameProduction(throttle);
 }
 
+void ProxyImpl::InitializeMutatorOnImpl(LayerTreeMutator* mutator) {
+  TRACE_EVENT0("cc,compositor-worker", "ProxyImpl::InitializeMutatorOnImpl");
+  DCHECK(IsImplThread());
+  layer_tree_host_impl_->SetLayerTreeMutator(mutator);
+}
+
 void ProxyImpl::UpdateTopControlsStateOnImpl(TopControlsState constraints,
                                              TopControlsState current,
                                              bool animate) {