Creating options page and storing preferences.

chrome/browser/resources/chromeos/switch_access/testable_switch_access.js

 // Copyright 2017 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.
 
 /**
  * Subclass of SwitchAccess that exposes SwitchAccess's methods for testing.
  */
 let TestableSwitchAccess = function() {
   SwitchAccess.call(this);
 };
 
 TestableSwitchAccess.prototype = {
   __proto__: SwitchAccess.prototype,
 
+  init_: function() {},
+
   getNextNode: function(node) {
     return this.getNextNode_(node);
   },
 
   getPreviousNode: function(node) {
     return this.getPreviousNode_(node);
   },
 
   getYoungestDescendant: function(node) {
     return this.getYoungestDescendant_(node);
   },
 
   isInteresting: function(node) {
     return this.isInteresting_(node);
   }
 };