Add a helper method to create SW SimpleEventCallbacks.

content/browser/service_worker/service_worker_version.h

Index: content/browser/service_worker/service_worker_version.h
diff --git a/content/browser/service_worker/service_worker_version.h b/content/browser/service_worker/service_worker_version.h
index f8f95eff88a97be3d681e9a1bebfb4d35c49b5d9..1d2e910cd37b35ac749e380b513a308e0c146b07 100644
--- a/content/browser/service_worker/service_worker_version.h
+++ b/content/browser/service_worker/service_worker_version.h
@@ -73,6 +73,8 @@ class CONTENT_EXPORT ServiceWorkerVersion
       public EmbeddedWorkerInstance::Listener {
  public:
   using StatusCallback = base::Callback<void(ServiceWorkerStatusCode)>;
+  using SimpleEventCallback =
+      base::Callback<void(ServiceWorkerStatusCode, base::Time)>;
 
   // Current version status; some of the status (e.g. INSTALLED and ACTIVATED)
   // should be persisted unlike running status.
@@ -275,6 +277,10 @@ class CONTENT_EXPORT ServiceWorkerVersion
   // was not found or the worker already terminated.
   bool FinishExternalRequest(const std::string& request_uuid);
 
+  // Creates a callback that is to be used for marking simple events dispatched
+  // through the ServiceWorkerEventDispatcher as finished for the |request_id|.
+  SimpleEventCallback CreateSimpleEventCallback(int request_id);
+
   // This must be called when the worker is running.
   mojom::ServiceWorkerEventDispatcher* event_dispatcher() {
     DCHECK(event_dispatcher_.is_bound());