[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());

[falken, 2017/05/24 08:24:18]

This is pretty tricky and I'm not sure with this change the tests in
resources/notificationclick-can-focus.js are still testing what they intended to
test.

But I don't have any ideas. I think the people originally involved with this
test are no longer working on service worker.

[leonhsl(Using Gerrit), 2017/05/25 00:16:39]

I believe this change does not change any behavior of those tests using this
synthesizeNotificationClick function.
They are calling waitUntil inside the returned promise's resolver function,
which executes on a microtask after completion of the event handler self's
execution. This is allowed before this CL, but now it's forbidden if has no any
other outstanding extend lifetime promise at that time, so I added such a new
call to waitUntil to ensure that.

             e.notification.close();
             self.removeEventListener('notificationclick', handler);
         };
 
         self.addEventListener('notificationclick', handler);
     });
 
     return promise;
 }