Take notification API out of experimental.

chrome/test/data/extensions/api_test/notifications/api/by_user/background.js

 // Copyright (c) 2012 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.
 
-const notification = chrome.experimental.notification;
+const notifications = chrome.experimental.notifications;
 var theOnlyTestDone = null;
 
 var notificationData = {
   templateType: "basic",
   iconUrl: "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAA" +
            "CNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHw" +
            "AAAABJRU5ErkJggg==",
   title: "Attention!",
   message: "Check out Cirque du Soleil"
 };
 
 var results = {
   FOO: false,
   BAR: true,
   BAT: false,
   BIFF: false,
   BLAT: true,
   BLOT: true
 };
 
 function createCallback(id) { }
 
 var onClosedHooks = {
   BIFF: function() {
-    notification.create("BLAT", notificationData, createCallback);
-    notification.create("BLOT", notificationData, createCallback);
+    notifications.create("BLAT", notificationData, createCallback);
+    notifications.create("BLOT", notificationData, createCallback);
   },
 };
 
 function onClosedListener(id, by_user) {
   if (results[id] !== by_user) {
     chrome.test.notifyFail("Notification " + id +
                            " closed with bad by_user param ( "+ by_user +" )");
     return;
   }
   chrome.test.notifyPass();
   delete results[id];
 
   if (typeof onClosedHooks[id] === "function")
     onClosedHooks[id]();
 
   if (Object.keys(results).length === 0)
     theOnlyTestDone();
 }
 
-notification.onClosed.addListener(onClosedListener);
+notifications.onClosed.addListener(onClosedListener);
 
 function theOnlyTest() {
   theOnlyTestDone = chrome.test.callbackAdded();
 
-  notification.create("FOO", notificationData, createCallback);
-  notification.create("BAR", notificationData, createCallback);
-  notification.create("BAT", notificationData, createCallback);
-  notification.create("BIFF", notificationData, createCallback);
+  notifications.create("FOO", notificationData, createCallback);
+  notifications.create("BAR", notificationData, createCallback);
+  notifications.create("BAT", notificationData, createCallback);
+  notifications.create("BIFF", notificationData, createCallback);
 }
 
 chrome.test.runTests([ theOnlyTest ]);