Introduce AnimationWorkletProxyClient and necessary plumbing to get it in worklet messaging proxy.

third_party/WebKit/Source/core/dom/CompositorProxy.cpp

Index: third_party/WebKit/Source/core/dom/CompositorProxy.cpp
diff --git a/third_party/WebKit/Source/core/dom/CompositorProxy.cpp b/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
index a10bd04a4ce429c33c94360da431956a69a58e2f..e715638b804f420fddba14fb52c421ec4cc444a1 100644
--- a/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
+++ b/third_party/WebKit/Source/core/dom/CompositorProxy.cpp
@@ -6,6 +6,7 @@
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
+#include "core/dom/CompositorWorkerProxyClient.h"
 #include "core/dom/DOMNodeIds.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContext.h"
@@ -123,7 +124,8 @@ CompositorProxy* CompositorProxy::create(ExecutionContext* context,
   if (context->isCompositorWorkerGlobalScope()) {
     WorkerClients* clients = toWorkerGlobalScope(context)->clients();
     DCHECK(clients);
-    CompositorProxyClient* client = CompositorProxyClient::from(clients);
+    CompositorWorkerProxyClient* client =
+        CompositorWorkerProxyClient::from(clients);
     return new CompositorProxy(elementId, compositorMutableProperties, client);
   }