Move ProtocolExtensionManager from SessionConnector into its own class

remoting/webapp/crd/js/session_connector.js

Index: remoting/webapp/crd/js/session_connector.js
diff --git a/remoting/webapp/crd/js/session_connector.js b/remoting/webapp/crd/js/session_connector.js
index d5c2d6c4baddc57758cc26f1e0a0463d42c01d66..fab0b3392509a8e1348535d6e1ce1b84c1f44487 100644
--- a/remoting/webapp/crd/js/session_connector.js
+++ b/remoting/webapp/crd/js/session_connector.js
@@ -98,12 +98,6 @@ remoting.SessionConnector.prototype.cancel = function() {};
 remoting.SessionConnector.prototype.getHostId = function() {};
 
 /**
- * @param {remoting.ProtocolExtension} extension
- */
-remoting.SessionConnector.prototype.registerProtocolExtension =
-    function(extension) {};
-
-/**
  * Closes the session and removes the plugin element.
  */
 remoting.SessionConnector.prototype.closeSession = function() {};