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

third_party/WebKit/Source/core/loader/EmptyClients.h

 /*
  * Copyright (C) 2006 Eric Seidel (eric@webkit.org)
  * Copyright (C) 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  * Copyright (C) 2012 Samsung Electronics. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 200 matching lines @@
   void updateTouchRectsForSubframeIfNecessary(LocalFrame* frame) override {}
   void setHasScrollEventHandlers(LocalFrame*, bool) override {}
 
   void setTouchAction(LocalFrame*, TouchAction) override {}
 
   void didAssociateFormControlsAfterLoad(LocalFrame*) override {}
 
   void annotatedRegionsChanged() override {}
   String acceptLanguages() override;
 
-  CompositorProxyClient* createCompositorProxyClient(LocalFrame*) override {
+  CompositorWorkerProxyClient* createCompositorWorkerProxyClient(
+      LocalFrame*) override {
     return nullptr;
   }
 
+  AnimationWorkletProxyClient* createAnimationWorkletProxyClient(
+      LocalFrame*) override {
+    return nullptr;
+  }
+
   void registerPopupOpeningObserver(PopupOpeningObserver*) override {}
   void unregisterPopupOpeningObserver(PopupOpeningObserver*) override {}
 
   std::unique_ptr<WebFrameScheduler> createFrameScheduler(
       BlameContext*) override;
 };
 
 class CORE_EXPORT EmptyFrameLoaderClient : public FrameLoaderClient {
   WTF_MAKE_NONCOPYABLE(EmptyFrameLoaderClient);
 
@@ skipping 224 matching lines @@
   Frame* nextSibling() const override { return nullptr; }
   Frame* firstChild() const override { return nullptr; }
   void frameFocused() const override {}
 };
 
 CORE_EXPORT void fillWithEmptyClients(Page::PageClients&);
 
 }  // namespace blink
 
 #endif  // EmptyClients_h