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..744a8f2f7c5f9af6e8ca37c1c7bba670b2f51447 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;
@@ -164,6 +165,9 @@ public:
 
     // Toggles scroll bottleneck rects on the HUD layer
     virtual void setShowScrollBottleneckRects(bool) { }
+
+    // Mutations are plumbed back to the layer tree via the mutator client.
+    virtual void setMutatorClient(std::unique_ptr<WebCompositorMutatorClient>) {}
 };
 
 } // namespace blink