setCurrentRange should ensure it moves ChromeVox to a valid range.

chrome/browser/resources/chromeos/chromevox/cvox2/background/background.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 The entry point for all ChromeVox2 related code for the
  * background page.
  */
 
 goog.provide('Background');
@@ skipping 317 matching lines @@
     return null;
   },
 
   /**
    * @override
    */
   setCurrentRange: function(newRange) {
     if (!this.inExcursion_ && newRange)
       this.savedRange_ = new cursors.Range(newRange.start, newRange.end);
 
+    if (newRange && !newRange.isValid())
+      return;
+
     this.currentRange_ = newRange;
     var oldMode = this.mode_;
     var newMode = this.getMode();
     if (oldMode != newMode) {
       this.onModeChanged_(newMode, oldMode);
       this.mode_ = newMode;
     }
 
     if (this.currentRange_) {
       var start = this.currentRange_.start.node;
@@ skipping 400 matching lines @@
   return new RegExp('^(' + globs.map(function(glob) {
     return glob.replace(/[.+^$(){}|[\]\\]/g, '\\$&')
         .replace(/\*/g, '.*')
         .replace(/\?/g, '.');
   }).join('|') + ')$');
 };
 
 new Background();
 
 });  // goog.scope