[ServiceWorker] Allow waitUntil to be called multiple times asynchronously

third_party/WebKit/LayoutTests/http/tests/serviceworker/chromium/resources/sw-test-helpers.js

 // Test helper that is meant as a mini test framework to be used from a service
 // worker that runs some tests and send results back to its client.
 //
 // A simple usage of this framework would consist of calling initialize() to
 // setup then runNextTestOrQuit() in order to start running the methods defined
 // by TESTS. Then, tests can start sending messages back to the client using
 // postMessage().
 //
 // Example:
 // var TESTS = [
@@ skipping 43 matching lines @@
 // object.
 self.synthesizeNotificationClick = function() {
     var promise = new Promise(function(resolve) {
         var title = "fake notification";
         registration.showNotification(title).then(function() {
             client.postMessage({type: 'click', title: title});
         });
 
         var handler = function(e) {
             resolve(e);
+            // To allow waitUntil to be called inside execution of the microtask
+            // enqueued by above resolve function.
+            e.waitUntil(Promise.resolve());
             e.notification.close();
             self.removeEventListener('notificationclick', handler);
         };
 
         self.addEventListener('notificationclick', handler);
     });
 
     return promise;
 }