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

third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp

Index: third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp
diff --git a/third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp b/third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp
index ee63ca4b447b59f86e832e79e5db6a4aede1714c..55973bb4d2b2daf563a77db7dffae8eef1f77c3b 100644
--- a/third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp
+++ b/third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp
@@ -5,8 +5,11 @@
 #include "modules/compositorworker/AnimationWorklet.h"
 
 #include "bindings/core/v8/V8Binding.h"
+#include "core/dom/AnimationWorkletProxyClient.h"
+#include "core/dom/CompositorProxyClientFactory.h"
 #include "core/dom/Document.h"
 #include "core/frame/LocalFrame.h"
+#include "core/page/ChromeClient.h"
 #include "modules/compositorworker/AnimationWorkletMessagingProxy.h"
 #include "modules/compositorworker/AnimationWorkletThread.h"
 
@@ -32,9 +35,16 @@ void AnimationWorklet::initialize() {
 
   DCHECK(!m_workletMessagingProxy);
   DCHECK(getExecutionContext());
+  Document* document = toDocument(getExecutionContext());
+  CompositorProxyClientFactory* clientFactory =
+      document->frame()->chromeClient().compositorProxyClientFactory(
+          document->frame());
+  AnimationWorkletProxyClient* proxyClient =
+      static_cast<AnimationWorkletProxyClient*>(
+          clientFactory->create(CompositorProxyClient::kWorkletClient));
 
   m_workletMessagingProxy =
-      new AnimationWorkletMessagingProxy(getExecutionContext());
+      new AnimationWorkletMessagingProxy(getExecutionContext(), proxyClient);
   m_workletMessagingProxy->initialize();
 }