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

third_party/WebKit/Source/web/ChromeClientImpl.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 196 matching lines @@
   void didCancelCompositionOnSelectionChange() override;
   void resetInputMethod() override;
   void showVirtualKeyboardOnElementFocus() override;
 
   void registerViewportLayers() const override;
 
   void showUnhandledTapUIIfNeeded(IntPoint, Node*, bool) override;
   void onMouseDown(Node*) override;
   void didUpdateBrowserControls() const override;
 
-  CompositorProxyClient* createCompositorProxyClient(LocalFrame*) override;
+  CompositorWorkerProxyClient* createCompositorWorkerProxyClient(
+      LocalFrame*) override;
+  AnimationWorkletProxyClient* createAnimationWorkletProxyClient(
+      LocalFrame*) override;
+
   FloatSize elasticOverscroll() const override;
 
   void didObserveNonGetFetchFromScript() const override;
 
   std::unique_ptr<WebFrameScheduler> createFrameScheduler(
       BlameContext*) override;
 
   double lastFrameTimeMonotonic() const override;
 
   void notifyPopupOpeningObservers() const;
@@ skipping 21 matching lines @@
 
 DEFINE_TYPE_CASTS(ChromeClientImpl,
                   ChromeClient,
                   client,
                   client->isChromeClientImpl(),
                   client.isChromeClientImpl());
 
 }  // namespace blink
 
 #endif