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

third_party/WebKit/Source/modules/compositorworker/AnimationWorkletMessagingProxy.h

Index: third_party/WebKit/Source/modules/compositorworker/AnimationWorkletMessagingProxy.h
diff --git a/third_party/WebKit/Source/modules/compositorworker/AnimationWorkletMessagingProxy.h b/third_party/WebKit/Source/modules/compositorworker/AnimationWorkletMessagingProxy.h
index 29789a99eff7a054e8fd0a606eb15832c4c9f4fb..fc30fd38163ec50ffd1c92fb512bf0216ec0d07e 100644
--- a/third_party/WebKit/Source/modules/compositorworker/AnimationWorkletMessagingProxy.h
+++ b/third_party/WebKit/Source/modules/compositorworker/AnimationWorkletMessagingProxy.h
@@ -5,6 +5,7 @@
 #ifndef AnimationWorkletMessagingProxy_h
 #define AnimationWorkletMessagingProxy_h
 
+#include "core/dom/AnimationWorkletProxyClient.h"
 #include "core/workers/ThreadedWorkletMessagingProxy.h"
 #include "wtf/Allocator.h"
 #include <memory>
@@ -19,12 +20,14 @@ class AnimationWorkletMessagingProxy final
   USING_FAST_MALLOC(AnimationWorkletMessagingProxy);
 
  public:
-  explicit AnimationWorkletMessagingProxy(ExecutionContext*);
+  explicit AnimationWorkletMessagingProxy(ExecutionContext*,

[nhiroki, 2016/11/24 06:59:00]

Can you remove 'explicit'?

[majidvp, 2016/11/28 14:43:21]

Done.

+                                          AnimationWorkletProxyClient*);
 
  protected:
   ~AnimationWorkletMessagingProxy() override;
 
   std::unique_ptr<WorkerThread> createWorkerThread(double originTime) override;
+  Persistent<AnimationWorkletProxyClient> m_proxyClient;
 };
 
 }  // namespace blink