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

third_party/WebKit/Source/modules/compositorworker/AnimationWorkletMessagingProxy.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef AnimationWorkletMessagingProxy_h
 #define AnimationWorkletMessagingProxy_h
 
+#include "core/dom/AnimationWorkletProxyClient.h"
 #include "core/workers/ThreadedWorkletMessagingProxy.h"
 #include "wtf/Allocator.h"
 #include <memory>
 
 namespace blink {
 
 class ExecutionContext;
 class WorkerThread;
 
 class AnimationWorkletMessagingProxy final
     : public ThreadedWorkletMessagingProxy {
   USING_FAST_MALLOC(AnimationWorkletMessagingProxy);
 
  public:
-  explicit AnimationWorkletMessagingProxy(ExecutionContext*);
+  AnimationWorkletMessagingProxy(ExecutionContext*,
+                                 AnimationWorkletProxyClient*);
 
  protected:
   ~AnimationWorkletMessagingProxy() override;
 
   std::unique_ptr<WorkerThread> createWorkerThread(double originTime) override;
+  Persistent<AnimationWorkletProxyClient> m_proxyClient;
 };
 
 }  // namespace blink
 
 #endif  // AnimationWorkletMessagingProxy_h