ServiceWorker: Add initial implementation of ExtendableMessageEvent behind a flag

content/browser/service_worker/service_worker_dispatcher_host.h

Index: content/browser/service_worker/service_worker_dispatcher_host.h
diff --git a/content/browser/service_worker/service_worker_dispatcher_host.h b/content/browser/service_worker/service_worker_dispatcher_host.h
index 89ff78997c2230277cd061c24c873fa41e5538e9..9d1ff96c7e22d5786193c936e83688c57666744b 100644
--- a/content/browser/service_worker/service_worker_dispatcher_host.h
+++ b/content/browser/service_worker/service_worker_dispatcher_host.h
@@ -138,6 +138,14 @@ class CONTENT_EXPORT ServiceWorkerDispatcherHost : public BrowserMessageFilter {
       int handle_id,
       const base::string16& message,
       const std::vector<TransferredMessagePort>& sent_message_ports);
+
+  // TODO(nhiroki): Remove this after ExtendableMessageEvent is enabled by
+  // default (crbug.com/543198).
+  void OnDeprecatedPostMessageToWorker(
+      int handle_id,
+      const base::string16& message,
+      const std::vector<TransferredMessagePort>& sent_message_ports);
+
   void OnTerminateWorker(int handle_id);
 
   ServiceWorkerRegistrationHandle* FindRegistrationHandle(