MD Settings: reduce complexity and overhead of prefs singleton

chrome/test/data/webui/settings/passwords_and_forms_browsertest.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.
 
 /** @fileoverview Runs the Polymer Passwords and Forms tests. */
 
 /** @const {string} Path to root from chrome/test/data/webui/settings/. */
 var ROOT_PATH = '../../../../../';
 
 // Polymer BrowserTest fixture.
@@ skipping 251 matching lines @@
 
   /**
    * @pram {boolean} autofill Whether autofill is enabled or not.
    * @param {boolean} passwords Whether passwords are enabled or not.
    * @return {!Promise<!Element>} The |prefs| object.
    */
   createPrefs: function(autofill, passwords) {
     return new Promise(function(resolve) {
       CrSettingsPrefs.deferInitialization = true;
       var prefs = document.createElement('settings-prefs');
-      document.body.appendChild(prefs);
-      prefs.initializeForTesting(new settings.FakeSettingsPrivate([
+      prefs.initialize(new settings.FakeSettingsPrivate([
         {
           key: 'autofill.enabled',
           type: chrome.settingsPrivate.PrefType.BOOLEAN,
           value: autofill,
         },
         {
           key: 'profile.password_manager_enabled',
           type: chrome.settingsPrivate.PrefType.BOOLEAN,
           value: passwords,
         },
@@ skipping 158 matching lines @@
         assertTrue(element.$.autofillManagerButton.hasAttribute('actionable'));
         assertTrue(element.$.passwordManagerButton.hasAttribute('actionable'));
 
         self.destroyPrefs(prefs);
       });
     });
   });
 
   mocha.run();
 });