Move ProtocolExtensionManager from SessionConnector into its own class

remoting/webapp/app_remoting/js/app_remoting.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.
 
 /**
  * @fileoverview
  * This class implements the functionality that is specific to application
  * remoting ("AppRemoting" or AR).
  */
 
@@ skipping 196 matching lines @@
 remoting.AppRemoting.prototype.onConnected_ = function(connectionInfo) {
   this.initSession_(connectionInfo);
 
   remoting.identity.getUserInfo().then(
       function(userInfo) {
         remoting.clientSession.sendClientMessage(
             'setUserDisplayInfo',
             JSON.stringify({fullName: userInfo.name}));
       });
 
-  this.sessionConnector_.registerProtocolExtension(this);
+  connectionInfo.plugin().extensions().register(this);
 
   this.connectedView_ = new remoting.AppConnectedView(
       document.getElementById('client-container'), connectionInfo);
 
   // Map Cmd to Ctrl on Mac since hosts typically use Ctrl for keyboard
   // shortcuts, but we want them to act as natively as possible.
   if (remoting.platformIsMac()) {
     connectionInfo.plugin().setRemapKeys('0x0700e3>0x0700e0,0x0700e7>0x0700e4');
   }
 };
@@ skipping 99 matching lines @@
 };
 
 /**
  * @return {string}
  * @private
  */
 remoting.AppRemoting.prototype.runApplicationUrl_ = function() {
   return remoting.settings.APP_REMOTING_API_BASE_URL + '/applications/' +
       remoting.settings.getAppRemotingApplicationId() + '/run';
 };