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

third_party/WebKit/Source/web/CompositorProxyClientFactoryImpl.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 "web/CompositorProxyClientFactoryImpl.h"
+
+#include "core/dom/CompositorProxyClient.h"
+#include "web/AnimationWorkletProxyClientImpl.h"
+#include "web/CompositorMutatorImpl.h"
+#include "web/CompositorWorkerProxyClientImpl.h"
+
+namespace blink {
+
+CompositorProxyClientFactoryImpl::CompositorProxyClientFactoryImpl(
+    CompositorMutatorImpl* mutator)
+    : m_mutator(mutator) {}
+
+CompositorProxyClient* CompositorProxyClientFactoryImpl::create(
+    CompositorProxyClient::Type type) {
+  switch (type) {
+    case CompositorProxyClient::kWorkerClient:
+      return new CompositorWorkerProxyClientImpl(m_mutator);
+    case CompositorProxyClient::kWorkletClient:
+      return new AnimationWorkletProxyClientImpl(m_mutator);
+  }
+
+  NOTREACHED() << "Unexpected CompositorProxyClient::Type: " << type;
+  return nullptr;
+}
+
+}  // namespace blink