Remove attach_ as publicly exposed method of Event.

chrome/renderer/resources/extensions/event.js

 // Copyright (c) 2012 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 eventNatives = requireNative('event_natives');
   var logging = requireNative('logging');
   var schemaRegistry = requireNative('schema_registry');
   var sendRequest = require('sendRequest').sendRequest;
   var utils = require('utils');
   var validate = require('schemaUtils').validate;
@@ skipping 501 matching lines @@
     'hasListener',
     'hasListeners',
     'getListenerCount',
     'dispatchToListener',
     'dispatch',
     'addRules',
     'removeRules',
     'getRules',
     // TODO(fsamuel): We really shouldn't be exposing these private methods
     // but certain tests rely on them.
-    'attach_',
     'dispatch_'
   ]);
 
   // NOTE: Event is (lazily) exposed as chrome.Event from dispatcher.cc.
   exports.Event = Event;
 
   exports.dispatchEvent = dispatchEvent;
   exports.parseEventOptions = parseEventOptions;
   exports.registerArgumentMassager = registerArgumentMassager;