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

third_party/WebKit/Source/core/page/ChromeClient.h

Index: third_party/WebKit/Source/core/page/ChromeClient.h
diff --git a/third_party/WebKit/Source/core/page/ChromeClient.h b/third_party/WebKit/Source/core/page/ChromeClient.h
index da058f6c2d165c6a213c255d0f0eb806d0677278..ffa4305de793b86a91c4ff7bf246e072fb6f9e03 100644
--- a/third_party/WebKit/Source/core/page/ChromeClient.h
+++ b/third_party/WebKit/Source/core/page/ChromeClient.h
@@ -50,7 +50,7 @@ class AXObject;
 class ColorChooser;
 class ColorChooserClient;
 class CompositorAnimationTimeline;
-class CompositorProxyClient;
+class CompositorProxyClientFactory;
 class DateTimeChooser;
 class DateTimeChooserClient;
 class Element;
@@ -317,7 +317,8 @@ class CORE_EXPORT ChromeClient : public HostWindow {
   virtual void registerPopupOpeningObserver(PopupOpeningObserver*) = 0;
   virtual void unregisterPopupOpeningObserver(PopupOpeningObserver*) = 0;
 
-  virtual CompositorProxyClient* createCompositorProxyClient(LocalFrame*) = 0;
+  virtual CompositorProxyClientFactory* compositorProxyClientFactory(
+      LocalFrame*) = 0;
 
   virtual FloatSize elasticOverscroll() const { return FloatSize(); }