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

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

-// 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.
-
-#include "core/dom/CompositorProxyClient.h"
-
-#include "platform/instrumentation/tracing/TraceEvent.h"
-
-namespace blink {
-
-CompositorProxyClient* CompositorProxyClient::from(WorkerClients* clients) {
-  return static_cast<CompositorProxyClient*>(
-      Supplement<WorkerClients>::from(clients, supplementName()));
-}
-
-const char* CompositorProxyClient::supplementName() {
-  return "CompositorProxyClient";
-}
-
-void provideCompositorProxyClientTo(WorkerClients* clients,
-                                    CompositorProxyClient* client) {
-  clients->provideSupplement(CompositorProxyClient::supplementName(), client);
-}
-
-}  // namespace blink