Improved error reporting in cryptotoken

chrome/browser/resources/cryptotoken/errorcodes.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.
 
 /**
- * @fileoverview Error codes reported by top-level request handlers.
+ * @fileoverview Errors reported by top-level request handlers.
  */
 'use strict';
 
 /**
  * Response status codes
  * @const
  * @enum {number}
  */
 var ErrorCodes = {
   'OK': 0,
   'OTHER_ERROR': 1,
   'BAD_REQUEST': 2,
   'CONFIGURATION_UNSUPPORTED': 3,
   'DEVICE_INELIGIBLE': 4,
   'TIMEOUT': 5
 };
+
+/**
+ * An error object for responses
+ * @typedef {{
+ *   errorCode: ErrorCodes,
+ *   errorMessage: (?string|undefined)
+ * }}
+ */
+var U2fError;