Added JSDoc to a function missing comment.

chrome/browser/resources/chromeos/login/oobe_screen_update.js

 // Copyright (c) 2011 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 Oobe update screen implementation.
  */
 
 cr.define('oobe', function() {
   /**
@@ skipping 29 matching lines @@
 
     /**
      * Buttons in oobe wizard's button strip.
      * @type {array} Array of Buttons.
      */
     get buttons() {
       return null;
     }
   };
 
+  /**
+   * Registers Escape accelerator to cancel update and
+   * makes 'press Escape to cancel update' hint visible.
+   */
   UpdateScreen.enableUpdateCancel = function() {
     $('update-cancel-hint').hidden = false;
     document.addEventListener('keydown', function(e) {
       if (e.keyCode == 27) {  // Escape
         var updateCancelHint = $('update-cancel-hint').children[0];
         updateCancelHint.textContent =
             localStrings.getString('cancelledUpdateMessage');
         chrome.send('cancelUpdate');
       }
     });
   };
 
   return {
     UpdateScreen: UpdateScreen
   };
 });