Revert of Revert of ServiceWorker: Use scheduler's default task queue for posting tasks on main thread

content/renderer/service_worker/embedded_worker_context_client.h

Index: content/renderer/service_worker/embedded_worker_context_client.h
diff --git a/content/renderer/service_worker/embedded_worker_context_client.h b/content/renderer/service_worker/embedded_worker_context_client.h
index 1f7ac8d4e64e89f757b80e42f016a87d6fc55291..89000a7a0cc49947679edfa38f868b7e0c9f4409 100644
--- a/content/renderer/service_worker/embedded_worker_context_client.h
+++ b/content/renderer/service_worker/embedded_worker_context_client.h
@@ -14,7 +14,7 @@
 #include "url/gurl.h"
 
 namespace base {
-class MessageLoopProxy;
+class SingleThreadTaskRunner;
 class TaskRunner;
 }
 
@@ -130,8 +130,8 @@
   // TODO: Implement DevTools related method overrides.
 
   int embedded_worker_id() const { return embedded_worker_id_; }
-  base::MessageLoopProxy* main_thread_proxy() const {
-    return main_thread_proxy_.get();
+  base::SingleThreadTaskRunner* main_thread_task_runner() const {
+    return main_thread_task_runner_.get();
   }
   ThreadSafeSender* thread_safe_sender() { return sender_.get(); }
 
@@ -148,7 +148,7 @@
   const GURL script_url_;
   const int worker_devtools_agent_route_id_;
   scoped_refptr<ThreadSafeSender> sender_;
-  scoped_refptr<base::MessageLoopProxy> main_thread_proxy_;
+  scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner_;
   scoped_refptr<base::TaskRunner> worker_task_runner_;
 
   scoped_ptr<ServiceWorkerScriptContext> script_context_;