Add some missing null checks in chromevox next.

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

Index: chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.js
diff --git a/chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.js b/chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.js
index 49c4416d8d3725eca09a7b4c40db6b6770bb1b8c..dd3c4ffeb14cb01bdc560c8be3ccff33f645bd34 100644
--- a/chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.js
+++ b/chrome/browser/resources/chromeos/chromevox/cvox2/background/desktop_automation_handler.js
@@ -67,7 +67,7 @@ DesktopAutomationHandler.prototype = {
 
     // 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 || '');
@@ -128,7 +128,8 @@ DesktopAutomationHandler.prototype = {
     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.