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

third_party/WebKit/Source/web/WebViewImpl.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 468 matching lines @@
                                   bool animate) override;
 
   BrowserControls& browserControls();
   // Called anytime browser controls layout height or content offset have
   // changed.
   void didUpdateBrowserControls();
 
   void forceNextWebGLContextCreationToFail() override;
   void forceNextDrawingBufferCreationToFail() override;
 
-  CompositorProxyClient* createCompositorProxyClient();
+  CompositorProxyClient* createCompositorProxyClient(
+      CompositorProxyClient::Type);
+
   IntSize mainFrameSize();
   WebDisplayMode displayMode() const { return m_displayMode; }
 
   PageScaleConstraintsSet& pageScaleConstraintsSet() const;
 
   FloatSize elasticOverscroll() const { return m_elasticOverscroll; }
 
   bool isTransparent() const;
   void setIsTransparent(bool value);
 
@@ skipping 241 matching lines @@
   Persistent<ResizeViewportAnchor> m_resizeViewportAnchor;
 };
 
 // We have no ways to check if the specified WebView is an instance of
 // WebViewImpl because WebViewImpl is the only implementation of WebView.
 DEFINE_TYPE_CASTS(WebViewImpl, WebView, webView, true, true);
 
 }  // namespace blink
 
 #endif