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

third_party/WebKit/Source/web/CompositorMutatorImpl.h

 // 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 CompositorMutatorImpl_h
 #define CompositorMutatorImpl_h
 
 #include "core/animation/CustomCompositorAnimationManager.h"
 #include "platform/graphics/CompositorMutator.h"
 #include "platform/heap/Handle.h"
 #include "platform/heap/HeapAllocator.h"
 #include "wtf/Noncopyable.h"
 #include <memory>
 
 namespace blink {
 
-class CompositorProxy;
-class CompositorProxyClientImpl;
+class CompositorAnimator;
 class CompositorMutatorClient;
 
-// Fans out requests from the compositor to all of the registered ProxyClients
-// which can then mutate layers through their CompositorProxy interfaces.
-// Requests for animation frames are received from ProxyClients and sent to the
-// compositor to generate a new compositor frame.
+// Fans out requests from the compositor to all of the registered
+// CompositorAnimators which can then mutate layers through their respective
+// mutate interface. Requests for animation frames are received from
+// CompositorAnimators and sent to the compositor to generate a new compositor
+// frame.
 //
 // Should be accessed only on the compositor thread.
 class CompositorMutatorImpl final : public CompositorMutator {
   WTF_MAKE_NONCOPYABLE(CompositorMutatorImpl);
 
  public:
   static std::unique_ptr<CompositorMutatorClient> createClient();
   static CompositorMutatorImpl* create();
 
   // CompositorMutator implementation.
   bool mutate(double monotonicTimeNow,
               CompositorMutableStateProvider*) override;
 
-  void registerProxyClient(CompositorProxyClientImpl*);
-  void unregisterProxyClient(CompositorProxyClientImpl*);
+  void registerCompositorAnimator(CompositorAnimator*);
+  void unregisterCompositorAnimator(CompositorAnimator*);
 
   void setNeedsMutate();
 
   void setClient(CompositorMutatorClient* client) { m_client = client; }
   CustomCompositorAnimationManager* animationManager() {
     return m_animationManager.get();
   }
 
  private:
   CompositorMutatorImpl();
 
-  using ProxyClients =
-      HashSet<CrossThreadPersistent<CompositorProxyClientImpl>>;
-  ProxyClients m_proxyClients;
+  using CompositorAnimators =
+      HashSet<CrossThreadPersistent<CompositorAnimator>>;
+  CompositorAnimators m_animators;
 
   std::unique_ptr<CustomCompositorAnimationManager> m_animationManager;
   CompositorMutatorClient* m_client;
 };
 
 }  // namespace blink
 
 #endif  // CompositorMutatorImpl_h