Move the Extension Port implementation out of messaging.js into its own file port.js.

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.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);
+  if (msg === undefined) {
+    // JSON.stringify can fail with unserializable objects. Log an error and
+    // drop the message.
+    //
+    // TODO(kalman/mpcomplete): it would be better to do the same validation
+    // here that we do for runtime.sendMessage (and variants), i.e. throw an
+    // schema validation Error, but just maintain the old behaviour until
+    // there's a good reason not to (http://crbug.com/263077).
+    console.error('Illegal argument to Port.postMessage');
+    return;
+  }
+  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_();
+  messagingNatives.PortRelease(this.portId_);
+};
+
+exports.Port = utils.expose('Port', Port, {
+  functions: ['disconnect', 'postMessage'],
+  properties: ['name', 'onDisconnect', 'onMessage']
+});