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

third_party/WebKit/Source/core/dom/CompositorWorkerProxyClient.h

Index: third_party/WebKit/Source/core/dom/CompositorWorkerProxyClient.h
diff --git a/third_party/WebKit/Source/core/dom/CompositorWorkerProxyClient.h b/third_party/WebKit/Source/core/dom/CompositorWorkerProxyClient.h
new file mode 100644
index 0000000000000000000000000000000000000000..7e25ccebe7a97be1d89450cec44b1d73720ef8b3
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+++ b/third_party/WebKit/Source/core/dom/CompositorWorkerProxyClient.h
@@ -0,0 +1,45 @@
+// 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 CompositorWorkerProxyClient_h
+#define CompositorWorkerProxyClient_h
+
+#include "core/CoreExport.h"
+#include "core/dom/CompositorProxyClient.h"
+#include "core/workers/WorkerClients.h"
+#include "wtf/Noncopyable.h"
+
+namespace blink {
+
+class WorkerClients;
+class WorkerGlobalScope;
+
+class CORE_EXPORT CompositorWorkerProxyClient
+    : public CompositorProxyClient,
+      public Supplement<WorkerClients> {
+  WTF_MAKE_NONCOPYABLE(CompositorWorkerProxyClient);
+  USING_GARBAGE_COLLECTED_MIXIN(CompositorWorkerProxyClient);
+
+ public:
+  CompositorWorkerProxyClient() {}
+  DEFINE_INLINE_VIRTUAL_TRACE() {
+    CompositorProxyClient::trace(visitor);
+    Supplement<WorkerClients>::trace(visitor);
+  }
+
+  static CompositorWorkerProxyClient* from(WorkerClients*);
+  static const char* supplementName();
+
+  virtual void dispose() = 0;
+  virtual void setGlobalScope(WorkerGlobalScope*) = 0;
+  virtual void requestAnimationFrame() = 0;
+};
+
+CORE_EXPORT void provideCompositorWorkerProxyClientTo(
+    WorkerClients*,
+    CompositorWorkerProxyClient*);
+
+}  // namespace blink
+
+#endif  // CompositorWorkerProxyClient_h