Fix broken parent->child link in automation webView.

chrome/renderer/resources/extensions/automation_custom_bindings.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.
 
 // Custom bindings for the automation API.
 var AutomationNode = require('automationNode').AutomationNode;
 var AutomationRootNode = require('automationNode').AutomationRootNode;
 var automation = require('binding').Binding.create('automation');
 var automationInternal =
     require('binding').Binding.create('automationInternal').generate();
@@ skipping 193 matching lines @@
   // browser process and set up a callback when it loads to attach that
   // tree as a child of this node and fire appropriate events.
   var childTreeID = GetIntAttribute(treeID, nodeID, 'childTreeId');
   if (!childTreeID)
     return;
 
   var subroot = AutomationRootNode.get(childTreeID);
   if (!subroot) {
     automationUtil.storeTreeCallback(childTreeID, function(root) {
       privates(root).impl.setHostNode(node);
-
+      privates(node).impl.childTree = root;
       if (root.docLoaded)
         privates(root).impl.dispatchEvent(schema.EventType.loadComplete);
 
       privates(node).impl.dispatchEvent(schema.EventType.childrenChanged);
     });
 
     automationInternal.enableFrame(childTreeID);
   } else {
     privates(subroot).impl.setHostNode(node);
+    privates(node).impl.childTree = subroot;
   }
 });
 
 automationInternal.onTreeChange.addListener(function(observerID,
                                                      treeID,
                                                      nodeID,
                                                      changeType) {
   var tree = AutomationRootNode.getOrCreate(treeID);
   if (!tree)
     return;
@@ skipping 91 matching lines @@
 });
 
 exports.binding = automation.generate();
 
 // Add additional accessibility bindings not specified in the automation IDL.
 // Accessibility and automation share some APIs (see
 // ui/accessibility/ax_enums.idl).
 forEach(schema, function(k, v) {
   exports.binding[k] = v;
 });