Ensure that privates are private.

chrome/renderer/resources/extensions/enterprise_platform_keys/token.js

 // Copyright 2014 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.
 
 var utils = require('utils');
 var SubtleCrypto = require('enterprise.platformKeys.SubtleCrypto').SubtleCrypto;
 
 /**
  * Implementation of enterprise.platformKeys.Token.
  * @param {string} id The id of the new Token.
  * @constructor
  */
 var TokenImpl = function(id) {
   this.id = id;
   this.subtleCrypto = new SubtleCrypto(id);
 };
 
-exports.Token =
-    utils.expose('Token', TokenImpl, {readonly:['id', 'subtleCrypto']});
+function Token() {
+  privates(Token).constructPrivate(this, arguments);
+}
+utils.expose(Token, TokenImpl, {
+  readonly: [
+    'id',
+    'subtleCrypto',
+  ],
+});
+
+exports.$set('Token', Token);