Revert of Update json_schema_compiler to handle the Automation extension API

chrome/browser/resources/chromeos/chromevox/cvox2/background/tree_walker.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 A tree walker over the automation tree.
  */
 
 goog.provide('AutomationTreeWalker');
 goog.provide('AutomationTreeWalkerPhase');
@@ skipping 70 matching lines @@
   this.phase_ = AutomationTreeWalkerPhase.INITIAL;
   /** @const {constants.Dir} @private */
   this.dir_ = dir;
   /** @const {!chrome.automation.AutomationNode} @private */
   this.initialNode_ = node;
   /**
    * Deepest common ancestor of initialNode and node. Valid only when moving
    * backward.
    * @type {chrome.automation.AutomationNode} @private
    */
-  this.backwardAncestor_ = node.parent || null;
+  this.backwardAncestor_ = node.parent;
   var restrictions = opt_restrictions || {};
 
   this.visitPred_ = function(node) {
     if (this.skipInitialAncestry_ &&
         this.phase_ == AutomationTreeWalkerPhase.ANCESTOR)
       return false;
 
     if (this.skipInitialSubtree_ &&
         this.phase != AutomationTreeWalkerPhase.ANCESTOR &&
         this.phase != AutomationTreeWalkerPhase.OTHER)
@@ skipping 112 matching lines @@
       node = node.previousSibling;
 
       while (!this.leafPred_(node) && node.lastChild)
         node = node.lastChild;
 
       this.node_ = node;
       return;
     }
     if (node.parent && this.backwardAncestor_ == node.parent) {
       this.phase_ = AutomationTreeWalkerPhase.ANCESTOR;
-      this.backwardAncestor_ = node.parent.parent || null;
+      this.backwardAncestor_ = node.parent.parent;
     }
-    this.node_ = node.parent || null;
+    this.node_ = node.parent;
   }
 };