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

third_party/WebKit/Source/web/WebFrameWidgetBase.h

Index: third_party/WebKit/Source/web/WebFrameWidgetBase.h
diff --git a/third_party/WebKit/Source/web/WebFrameWidgetBase.h b/third_party/WebKit/Source/web/WebFrameWidgetBase.h
index 4d0e84d79177a3881b8eff40406212565a94b29c..40096cfafb7f8f790ff0ec4f1f5a6fea62a58e06 100644
--- a/third_party/WebKit/Source/web/WebFrameWidgetBase.h
+++ b/third_party/WebKit/Source/web/WebFrameWidgetBase.h
@@ -6,6 +6,8 @@
 #define WebFrameWidgetBase_h
 
 #include "core/clipboard/DataObject.h"
+#include "core/dom/CompositorProxyClient.h"
+
 #include "public/platform/WebDragData.h"
 #include "public/web/WebFrameWidget.h"
 #include "wtf/Assertions.h"
@@ -13,7 +15,6 @@
 namespace blink {
 
 class CompositorAnimationHost;
-class CompositorProxyClient;
 class GraphicsLayer;
 class WebImage;
 class WebLayer;
@@ -26,7 +27,8 @@ class WebFrameWidgetBase : public WebFrameWidget {
  public:
   virtual bool forSubframe() const = 0;
   virtual void scheduleAnimation() = 0;
-  virtual CompositorProxyClient* createCompositorProxyClient() = 0;
+  virtual CompositorProxyClient* createCompositorProxyClient(
+      CompositorProxyClient::Type) = 0;
   virtual WebWidgetClient* client() const = 0;
 
   // Sets the root graphics layer. |GraphicsLayer| can be null when detaching