Fix flaky SW registration in PushMessaging/BudgetManager browser tests

chrome/test/data/push_messaging/push_test.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 'use strict';
 
 // The ResultQueue is a mechanism for passing messages back to the test
 // framework.
 var resultQueue = new ResultQueue();
 
@@ skipping 26 matching lines @@
 function requestNotificationPermission() {
   Notification.requestPermission(function(permission) {
     sendResultToTest('permission status - ' + permission);
   });
 }
 
 function registerServiceWorker() {
   // The base dir used to resolve service_worker.js and the scope depends on
   // whether this script is included from an html file in ./, subscope1/, or
   // subscope2/.
-  navigator.serviceWorker.register('service_worker.js', {scope: './'}).then(
-      function(swRegistration) {
-        sendResultToTest('ok - service worker registered');
-      }, sendErrorToTest);
+  navigator.serviceWorker.register('service_worker.js', {
+    scope: './'
+  }).then(swRegistrationReady).then(() => {
+    sendResultToTest('ok - service worker registered');
+  }).catch(sendErrorToTest);
 }
 
 function unregisterServiceWorker() {
   navigator.serviceWorker.getRegistration().then(function(swRegistration) {
     swRegistration.unregister().then(function(result) {
       sendResultToTest('service worker unregistration status: ' + result);
     })
   }).catch(sendErrorToTest);
 }
 
@@ skipping 143 matching lines @@
   }).catch(sendErrorToTest);
 }
 
 navigator.serviceWorker.addEventListener('message', function(event) {
   var message = JSON.parse(event.data);
   if (message.type == 'push')
     resultQueue.push(message.data);
   else
     sendResultToTest(message.data);
 }, false);