Automation API: Get rid of host node and get parent from C++ bindings instead

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 206 matching lines @@
   if (!childTreeID)
     return;
 
   var subroot = AutomationRootNode.get(childTreeID);
   if (!subroot || subroot.role == 'unknown') {
     automationUtil.storeTreeCallback(childTreeID, function(root) {
       // Return early if the root has already been attached.
       if (root.parent)
         return;
 
-      privates(root).impl.setHostNode(node);
-
       if (root.docLoaded) {
         privates(root).impl.dispatchEvent('loadComplete', 'page');
       }
 
       privates(node).impl.dispatchEvent('childrenChanged', 'none');
     });
 
     automationInternal.enableFrame(childTreeID);
-  } else {
-    privates(subroot).impl.setHostNode(node);
   }
 });
 
 automationInternal.onTreeChange.addListener(function(observerID,
                                                      treeID,
                                                      nodeID,
                                                      changeType) {
   var tree = AutomationRootNode.getOrCreate(treeID);
   if (!tree)
     return;
@@ skipping 106 matching lines @@
   DestroyAccessibilityTree(id);
 });
 
 automationInternal.onAccessibilityTreeSerializationError.addListener(
     function(id) {
   automationInternal.enableFrame(id);
 });
 
 var binding = automation.generate();
 exports.$set('binding', binding);