Fix crash when accessing automation node from stale AX tree

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 IsInteractPermitted =
     requireNative('automationInternal').IsInteractPermitted;
 
@@ skipping 739 matching lines @@
   hostNode_: null,
 
   /**
    * A map from id to AutomationNode.
    * @type {Object.<number, AutomationNode>}
    * @private
    */
   axNodeDataCache_: null,
 
   get id() {
-    return GetRootID(this.treeID);
+    var result = GetRootID(this.treeID);
+
+    // Don't return undefined, because the id is often passed directly
+    // as an argument to a native binding that expects only a valid number.
+    if (result === undefined)
+      return -1;
+
+    return result;
   },
 
   get: function(id) {
     if (id == undefined)
       return undefined;
 
     if (id == this.id)
       return this.wrapper;
 
     var obj = this.axNodeDataCache_[id];
@@ skipping 89 matching lines @@
 AutomationRootNode.getOrCreate = function(treeID) {
   return AutomationRootNodeImpl.getOrCreate(treeID);
 }
 
 AutomationRootNode.destroy = function(treeID) {
   AutomationRootNodeImpl.destroy(treeID);
 }
 
 exports.AutomationNode = AutomationNode;
 exports.AutomationRootNode = AutomationRootNode;