Add some missing null checks in chromevox next.

chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.js

 // Copyright 2015 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 Handles automation from a desktop automation node.
  */
 
 goog.provide('DesktopAutomationHandler');
 
@@ skipping 49 matching lines @@
 
     if (!node)
       return;
 
     var prevRange = global.backgroundObj.currentRange;
 
     global.backgroundObj.currentRange = cursors.Range.fromNode(node);
 
     // Check to see if we've crossed roots. Continue if we've crossed roots or
     // are not within web content.
-    if (node.root.role == 'desktop' ||
+    if (node.root.role == RoleType.desktop ||
         !prevRange ||
         prevRange.start.node.root != node.root)
       global.backgroundObj.refreshMode(node.root.docUrl || '');
 
     // Don't process nodes inside of web content if ChromeVox Next is inactive.
     if (node.root.role != RoleType.desktop &&
         global.backgroundObj.mode === ChromeVoxMode.CLASSIC) {
       chrome.accessibilityPrivate.setFocusRing([]);
       return;
     }
@@ skipping 40 matching lines @@
     var node = evt.target;
 
     // Discard focus events on embeddedObject nodes.
     if (node.role == RoleType.embeddedObject)
       return;
 
     // It almost never makes sense to place focus directly on a rootWebArea.
     if (node.role == RoleType.rootWebArea) {
       // Discard focus events for root web areas when focus was previously
       // placed on a descendant.
-      if (global.backgroundObj.currentRange.start.node.root == node)
+      var currentRange = global.backgroundObj.currentRange;
+      if (currentRange && currentRange.start.node.root == node)
         return;
 
       // Discard focused root nodes without focused state set.
       if (!node.state.focused)
         return;
 
       // Try to find a focusable descendant.
       node = node.find({state: {focused: true}}) || node;
     }
 
@@ skipping 141 matching lines @@
   if (cvox.ChromeVox.isMac)
     return;
   chrome.automation.getDesktop(function(desktop) {
     global.desktopAutomationHandler = new DesktopAutomationHandler(desktop);
   });
 };
 
 DesktopAutomationHandler.init_();
 
 });  // goog.scope