Fix crash in Chromevox event handling

chrome/browser/resources/chromeos/chromevox/common/dom_util.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 A collection of JavaScript utilities used to simplify working
  * with the DOM.
  */
 
 
@@ skipping 212 matching lines @@
  * @param {Node} root The root of the subtree to check.
  * @param {boolean} recursive Whether or not to check beyond the root of the
  *     subtree for visible nodes. This option exists for performance tuning.
  *     Sometimes we already have information about the descendants, and we do
  *     not need to check them again.
  * @return {boolean} True if the subtree contains a visible node.
  * @private
  */
 cvox.DomUtil.hasVisibleNodeSubtree_ = function(root, recursive) {
   if (!(root instanceof Element)) {
+    if (!root.parentElement) {
+      return false;
+    }
     var parentStyle = document.defaultView
         .getComputedStyle(root.parentElement, null);
     var isVisibleParent = !cvox.DomUtil.isInvisibleStyle(parentStyle);
     return isVisibleParent;
   }
 
   var rootStyle = document.defaultView.getComputedStyle(root, null);
   var isRootVisible = !cvox.DomUtil.isInvisibleStyle(rootStyle);
   if (isRootVisible) {
     return true;
@@ skipping 2354 matching lines @@
         var describedNode = document.getElementById(describedById);
         if (describedNode) {
           desc += ' ' + cvox.DomUtil.getName(
               describedNode, true, true, true);
         }
       }
     }
   }
   return desc;
 };