Sanitize inheritance in callers of utils.expose

chrome/renderer/resources/extensions/automation/automation_event.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 utils = require('utils');
 
-var AutomationEventImpl = function(type, target) {
+function AutomationEventImpl(type, target) {
   this.propagationStopped = false;
 
   // TODO(aboxhall): make these read-only properties
   this.type = type;
   this.target = target;
   this.eventPhase = Event.NONE;
-};
+}
 
 AutomationEventImpl.prototype = {
+  __proto__: null,
   stopPropagation: function() {
     this.propagationStopped = true;
-  }
+  },
 };
 
 function AutomationEvent() {
   privates(AutomationEvent).constructPrivate(this, arguments);
 }
 utils.expose(AutomationEvent, AutomationEventImpl, {
   functions: [
     'stopPropagation',
   ],
   readonly: [
     'type',
     'target',
     'eventPhase',
   ],
 });
 
 exports.$set('AutomationEvent', AutomationEvent);