Fix broken parent->child link in automation webView.

chrome/renderer/resources/extensions/automation/automation_node.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.
 
 var AutomationEvent = require('automationEvent').AutomationEvent;
 var automationInternal =
     require('binding').Binding.create('automationInternal').generate();
 var exceptionHandler = require('uncaught_exception_handler');
 var IsInteractPermitted =
     requireNative('automationInternal').IsInteractPermitted;
@@ skipping 223 matching lines @@
   },
 
   boundsForRange: function(startIndex, endIndex) {
     return GetBoundsForRange(this.treeID, this.id, startIndex, endIndex);
   },
 
   get indexInParent() {
     return GetIndexInParent(this.treeID, this.id);
   },
 
+  set childTree(node) {
+    this.childTree_ = node;
+  },
+
   get childTree() {
-    var childTreeID = GetIntAttribute(this.treeID, this.id, 'childTreeId');
-    if (childTreeID)
-      return AutomationRootNodeImpl.get(childTreeID);
+    return this.childTree_;
   },
 
   get firstChild() {
     if (this.childTree)
       return this.childTree;
     if (!GetChildCount(this.treeID, this.id))
       return undefined;
     var firstChildID = GetChildIDAtIndex(this.treeID, this.id, 0);
     return this.rootImpl.get(firstChildID);
   },
@@ skipping 727 matching lines @@
 AutomationRootNode.getOrCreate = function(treeID) {
   return AutomationRootNodeImpl.getOrCreate(treeID);
 }
 
 AutomationRootNode.destroy = function(treeID) {
   AutomationRootNodeImpl.destroy(treeID);
 }
 
 exports.AutomationNode = AutomationNode;
 exports.AutomationRootNode = AutomationRootNode;