Added unit tests for switch_access.js.

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,
+
+  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);
+  }
+};