Fix NotificationUIManagerTest::testShowAndCloseMultipleNotifications.

chrome/test/data/notifications/notification_test_utils.js

 // Copyright 2015 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.
 
+var activatedServiceWorkerPromise = null;
+
 // Returns a promise that will be resolved with an activated Service
 // Worker, or rejects when the Service Worker could not be started. There
 // will be a message port to and from the worker in |messagePort|.
 function GetActivatedServiceWorker(script, scope) {
-  return navigator.serviceWorker.getRegistration(scope)
-      .then(function(registration) {
-        // Unregister any existing Service Worker.
-        if (registration)
-          return registration.unregister();
-      }).then(function() {
-        // Register the Service Worker again.
-        return navigator.serviceWorker.register(script, { scope: scope });
-      }).then(function(registration) {
-        if (registration.active) {
-          return registration;
-        } else if (registration.waiting || registration.installing) {
-          var worker = registration.waiting || registration.installing;
+  if (activatedServiceWorkerPromise == null) {
+    activatedServiceWorkerPromise =
+        navigator.serviceWorker.getRegistration(scope)
+        .then(function(registration) {
+          // Unregister any existing Service Worker.
+          if (registration)
+            return registration.unregister();
+        }).then(function() {
+          // Register the Service Worker again.
+          return navigator.serviceWorker.register(script, { scope: scope });
+        }).then(function(registration) {
+          if (registration.active) {
+            return registration;
+          } else if (registration.waiting || registration.installing) {
+            var worker = registration.waiting || registration.installing;
+            return new Promise(function(resolve) {
+              worker.addEventListener('statechange', function () {
+                if (worker.state === 'activated')
+                  resolve(registration);
+              });
+            });
+          } else {
+            return Promise.reject('Service Worker in invalid state.');
+          }
+        }).then(function(registration) {
           return new Promise(function(resolve) {
-            worker.addEventListener('statechange', function () {
-              if (worker.state === 'activated')
+            var channel = new MessageChannel();
+            channel.port1.addEventListener('message', function(event) {
+              if (event.data == 'ready')
                 resolve(registration);
             });
+
+            registration.active.postMessage(channel.port2,
+                                            [ channel.port2 ]);
+
+            messagePort = channel.port1;
+            messagePort.start();
           });
-        } else {
-          return Promise.reject('Service Worker in invalid state.');
-        }
-      }).then(function(registration) {
-        return new Promise(function(resolve) {
-          var channel = new MessageChannel();
-          channel.port1.addEventListener('message', function(event) {
-            if (event.data == 'ready')
-              resolve(registration);
-          });
+        });
+  }
 
-          registration.active.postMessage(channel.port2,
-                                          [ channel.port2 ]);
-
-          messagePort = channel.port1;
-          messagePort.start();
-        });
-      });
+  return activatedServiceWorkerPromise;
 }