Clear the onMessage and onDisconnect listeners when their Extension Port is destroyed.

extensions/renderer/resources/port.js

 // Copyright 2015 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 Event = require('event_bindings').Event;
 var messagingNatives = requireNative('messaging_natives');
 var utils = require('utils');
 
 // Port object.  Represents a connection to another script context through
 // which messages can be passed.
 function Port(portId, opt_name) {
   this.portId_ = portId;
   this.name = opt_name;
 
   var portSchema = {name: 'port', $ref: 'runtime.Port'};
   var messageSchema = {name: 'message', type: 'any', optional: true};
   var options = {unmanaged: true};
 
+  this.onMessage = new Event(null, [messageSchema, portSchema], options);
   this.onDisconnect = new Event(null, [portSchema], options);
-  this.onMessage = new Event(null, [messageSchema, portSchema], options);
   this.onDestroy_ = null;
 }
 
 // Sends a message asynchronously to the context on the other end of this
 // port.
 Port.prototype.postMessage = function(msg) {
   // JSON.stringify doesn't support a root object which is undefined.
   if (msg === undefined)
     msg = null;
   msg = $JSON.stringify(msg);
@@ skipping 11 matching lines @@
   messagingNatives.PostMessage(this.portId_, msg);
 };
 
 // Disconnects the port from the other end.
 Port.prototype.disconnect = function() {
   messagingNatives.CloseChannel(this.portId_, true);
   this.destroy_();
 };
 
 Port.prototype.destroy_ = function() {
-  // Note: it's not necessary to destroy the onDisconnect/onMessage events
-  // because they're unmanaged.
   if (this.onDestroy_)
     this.onDestroy_();
+  // Destroy the onMessage/onDisconnect events in case the extension added
+  // listeners, but didn't remove them, when the port closed.
+  privates(this.onMessage).impl.destroy_();
+  privates(this.onDisconnect).impl.destroy_();
   messagingNatives.PortRelease(this.portId_);
 };
 
 exports.Port = utils.expose('Port', Port, {
   functions: ['disconnect', 'postMessage'],
-  properties: ['name', 'onDisconnect', 'onMessage']
+  properties: ['name', 'onMessage', 'onDisconnect']
 });