Fix warnings and errors in ChromeVox since Closure compiler update.

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 164 matching lines @@
         if (node)
           current = cursors.Range.fromNode(node);
         break;
       case 'doDefault':
         if (this.currentRange_)
           this.currentRange_.getStart().getNode().doDefault();
         break;
       case 'continuousRead':
         global.isReadingContinuously = true;
         var continueReading = function(prevRange) {
-          if (!global.isReadingContinuously)
+          if (!global.isReadingContinuously || !this.currentRange_)
             return;
 
           new Output().withSpeechAndBraille(
                   this.currentRange_, prevRange, Output.EventType.NAVIGATE)
               .onSpeechEnd(function() { continueReading(prevRange); })
               .go();
           prevRange = this.currentRange_;
           this.currentRange_ =
               this.currentRange_.move(cursors.Unit.NODE, Dir.FORWARD);
 
-          if (this.currentRange_.equals(prevRange))
+          if (!this.currentRange_ || this.currentRange_.equals(prevRange))
             global.isReadingContinuously = false;
         }.bind(this);
 
         continueReading(null);
         return;
     }
 
     if (pred) {
       var node = AutomationUtil.findNextNode(
           current.getBound(dir).getNode(), dir, pred);
@@ skipping 228 matching lines @@
         }.bind(this));
       }
     }.bind(this));
   }
 };
 
 /** @type {Background} */
 global.backgroundObj = new Background();
 
 });  // goog.scope