Fix warnings and errors in ChromeVox since Closure compiler update.

chrome/browser/resources/chromeos/chromevox/common/chromevox_json.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.
 
 goog.provide('cvox.ChromeVoxJSON');
 
 
 /**
  * @fileoverview A simple wrapper around the JSON APIs.
  * If it is possible to use the browser's built in native JSON, then
  * cvox.ChromeVoxJSON is the same as JSON.
  * If the page has its own version of JSON, cvox.ChromeVoxJSON will use its
  * own implementation (rather than the version of JSON on the page
  * which may be outdated/broken).
  */
 
 if (!cvox.ChromeVoxJSON) {
-  /**
-   * @type {Object}
-   */
+  /** Placeholder object. */
   cvox.ChromeVoxJSON = {};
 }
 
 if (window.JSON && window.JSON.toString() == '[object JSON]') {
   cvox.ChromeVoxJSON = window.JSON;
 } else {
   /*
    *  JSON implementation renamed to cvox.ChromeVoxJSON.
    *  This only gets called if the page has its own version of JSON.
    *
@@ skipping 330 matching lines @@
           return typeof reviver === 'function' ? walk({'': j}, '') : j;
         }
 
         // If the text is not JSON parseable, then a SyntaxError is thrown.
 
         throw new SyntaxError('JSON.parse');
       };
     }
   }());
 }