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 a66bb7b6af4e0500191abac41bb01a87d75b8b64..6c8770c4bbaa31af09eaa95e04da0a3c680538c3 100644
--- a/third_party/WebKit/public/platform/WebLayerTreeView.h
+++ b/third_party/WebKit/public/platform/WebLayerTreeView.h
@@ -28,6 +28,7 @@
 
 #include "WebColor.h"
 #include "WebCommon.h"
+#include "WebCompositorMutatorClient.h"
 #include "WebEventListenerProperties.h"
 #include "WebFloatPoint.h"
 #include "WebNonCopyable.h"
@@ -145,6 +146,9 @@ 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) { };