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

third_party/WebKit/public/platform/WebLayerTreeView.h

Index: third_party/WebKit/public/platform/WebLayerTreeView.h
diff --git a/third_party/WebKit/public/platform/WebLayerTreeView.h b/third_party/WebKit/public/platform/WebLayerTreeView.h
index c902c88c9634bd0eab843c6355d6f72d92e02fad..625478655e95ec63e896648384ba1f22d72f9208 100644
--- a/third_party/WebKit/public/platform/WebLayerTreeView.h
+++ b/third_party/WebKit/public/platform/WebLayerTreeView.h
@@ -44,6 +44,7 @@ class AnimationTimeline;
 namespace blink {
 
 class WebCompositeAndReadbackAsyncCallback;
+class WebCompositorMutatorClient;
 class WebLayer;
 class WebLayoutAndPaintAsyncCallback;
 struct WebPoint;
@@ -142,6 +143,9 @@ public:
     virtual void registerSelection(const WebSelection&) { }
     virtual void clearSelection() { }
 
+    // Mutations are plumbed back to the layer tree via the mutator client.
+    virtual void setMutatorClient(std::unique_ptr<WebCompositorMutatorClient>) {}
+
     // Input properties ---------------------------------------------------
     virtual void setEventListenerProperties(WebEventListenerClass, WebEventListenerProperties) { };
     virtual void setHaveScrollEventHandlers(bool) { };