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 89e497661409a817837a561c80fde17e6cb1e468..00ba3bee5fec17900daf8ede7b4a11a6c775f62d 100644
--- a/third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp
+++ b/third_party/WebKit/Source/modules/compositorworker/AnimationWorklet.cpp
@@ -5,8 +5,10 @@
 #include "modules/compositorworker/AnimationWorklet.h"
 
 #include "bindings/core/v8/V8Binding.h"
+#include "core/dom/AnimationWorkletProxyClient.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"
 
@@ -30,9 +32,15 @@ void AnimationWorklet::initialize() {
 
   DCHECK(!m_workletMessagingProxy);
   DCHECK(getExecutionContext());
+  Document* document = toDocument(getExecutionContext());
+  CompositorProxyClient* client =
+      document->frame()->chromeClient().createCompositorProxyClient(
+          CompositorProxyClient::kWorkletClient, document->frame());
+  AnimationWorkletProxyClient* proxyClient =
+      static_cast<AnimationWorkletProxyClient*>(client);

[dcheng, 2017/01/24 22:56:26]

Rather than downcasting here and below, we should just have two separate
functions IMO. While it costs us an extra vtable entry, it's more robust against
programmer error.

[majidvp, 2017/01/26 15:00:04]

This means adding two methods to more than a few places (ChromeClient and its
impls RenderWidgetFrameBase and its impls). Perhaps we can achieve the same
robustness by doing safer typecasts via DEFINE_TYPE_CASTS? This seems to be a
fairly typical pattern in Blink. I prefer this option if you are open to it.

 
   m_workletMessagingProxy =
-      new AnimationWorkletMessagingProxy(getExecutionContext());
+      new AnimationWorkletMessagingProxy(getExecutionContext(), proxyClient);
   m_workletMessagingProxy->initialize();
 }