Add some missing null checks in chromevox next.

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 116 matching lines @@
 
   chrome.automation.addTreeChangeObserver(this.onTreeChange);
 };
 
 Background.prototype = {
   /** Forces ChromeVox Next to be active for all tabs. */
   forceChromeVoxNextActive: function() {
     this.setChromeVoxMode(ChromeVoxMode.FORCE_NEXT);
   },
 
+  /** @type {ChromeVoxMode} */
   get mode() {
     return this.mode_;
   },
 
+  /** @type {cursors.Range} */
   get currentRange() {
     return this.currentRange_;
   },
 
   set currentRange(value) {
     if (!value)
       return;
 
     this.currentRange_ = value;
   },
@@ skipping 448 matching lines @@
     chrome.tabs.query({active: true}, function(tabs) {
       if (mode === ChromeVoxMode.CLASSIC) {
         // Generally, we don't want to inject classic content scripts as it is
         // done by the extension system at document load. The exception is when
         // we toggle classic on manually as part of a user command.
         if (opt_injectClassic)
           cvox.ChromeVox.injectChromeVoxIntoTabs(tabs);
       } else {
         // When in compat mode, if the focus is within the desktop tree proper,
         // then do not disable content scripts.
-        if (this.currentRange_.start.node.root.role == 'desktop')
+        if (this.currentRange_ &&
+            this.currentRange_.start.node.root.role == RoleType.desktop)
           return;
 
         this.disableClassicChromeVox_();
       }
     }.bind(this));
 
     this.mode_ = mode;
   },
 
   /**
@@ skipping 62 matching lines @@
     return glob.replace(/[.+^$(){}|[\]\\]/g, '\\$&')
         .replace(/\*/g, '.*')
         .replace(/\?/g, '.');
   }).join('|') + ')$');
 };
 
 /** @type {Background} */
 global.backgroundObj = new Background();
 
 });  // goog.scope