Added auto-scan, made some small changes to how prefs are stored, refactored.

chrome/browser/resources/chromeos/switch_access/switch_access_interface.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.
+
+/**
+ * Interface for controllers to interact with main SwitchAccess class.
+ *
+ * @interface
+ */
+let SwitchAccessInterface = function() {
+  /**
+   * @type {SwitchAccessPrefs}
+   */
+  this.switchAccessPrefs = null;
+};
+
+SwitchAccessInterface.prototype = {
+  moveToNext: function() {},
+
+  moveToPrevious: function() {},
+
+  doDefault: function() {},
+
+  showOptionsPage: function() {},
+
+  performedUserAction: function() {},
+
+  debugMoveToNext: function() {},
+
+  debugMoveToPrevious: function() {},
+
+  debugMoveToFirstChild: function() {},
+
+  debugMoveToParent: function() {}
+};