Fix crash in Chromevox event handling

chrome/browser/resources/chromeos/chromevox/common/dom_util.js

Index: chrome/browser/resources/chromeos/chromevox/common/dom_util.js
diff --git a/chrome/browser/resources/chromeos/chromevox/common/dom_util.js b/chrome/browser/resources/chromeos/chromevox/common/dom_util.js
index d8a5e246ca2d331c33ab7bf3b5f7e4b9d138f754..f27290da55b62cebd46ae5e5baa392959e43206d 100644
--- a/chrome/browser/resources/chromeos/chromevox/common/dom_util.js
+++ b/chrome/browser/resources/chromeos/chromevox/common/dom_util.js
@@ -230,6 +230,9 @@ cvox.DomUtil.hasInvisibleAncestor_ = function(node) {
  */
 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);