Add a helper method to create SW SimpleEventCallbacks.

content/browser/service_worker/service_worker_version.cc

Index: content/browser/service_worker/service_worker_version.cc
diff --git a/content/browser/service_worker/service_worker_version.cc b/content/browser/service_worker/service_worker_version.cc
index 470addbdb2ef05251d331c31f24fa90329102272..db50a469db16e87eeb60afb5b3d4156b18f12911 100644
--- a/content/browser/service_worker/service_worker_version.cc
+++ b/content/browser/service_worker/service_worker_version.cc
@@ -618,6 +618,14 @@ bool ServiceWorkerVersion::FinishExternalRequest(
   return true;
 }
 
+ServiceWorkerVersion::SimpleEventCallback
+ServiceWorkerVersion::CreateSimpleEventCallback(int request_id) {
+  // The weak reference to |this| is safe because storage of the callbacks, the
+  // pending responses of the ServiceWorkerEventDispatcher, is owned by |this|.
+  return base::Bind(&ServiceWorkerVersion::OnSimpleEventFinished,
+                    base::Unretained(this), request_id);
+}
+
 void ServiceWorkerVersion::RunAfterStartWorker(
     ServiceWorkerMetrics::EventType purpose,
     const base::Closure& task,