Fix flaky SW registration in PushMessaging/BudgetManager browser tests

chrome/test/data/budget_service/budget_test.js

 // Copyright 2016 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();
 
+// Waits for the given ServiceWorkerRegistration to become ready.
+// Shim for https://github.com/w3c/ServiceWorker/issues/770.
+function swRegistrationReady(reg) {
+  return new Promise((resolve, reject) => {
+    if (reg.active) {
+      resolve();
+      return;
+    }
+
+    if (!reg.installing && !reg.waiting) {
+      reject(Error('Install failed'));
+      return;
+    }
+
+    (reg.installing || reg.waiting).addEventListener('statechange', function() {
+      if (this.state == 'redundant') {
+        reject(Error('Install failed'));
+      } else if (this.state == 'activated') {
+        resolve();
+      }
+    });
+  });
+}
+
 function registerServiceWorker() {
   // The base dir used to resolve service_worker.js.
-  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);
 }
 
 // Query for the budget and return the current total.
 function documentGetBudget() {
   navigator.budget.getBudget().then(function(budget) {
     sendResultToTest("ok - budget returned value of " + budget[0].budgetAt);
   }, function() {
     sendResultToTest("failed - unable to get budget values");
   });
 }
@@ skipping 26 matching lines @@
   }
 }
 
 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);