[Chromoting] Implement HostExperimentSessionPlugin

remoting/protocol/session_plugin.h

 // Copyright 2016 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.
 
 #ifndef REMOTING_PROTOCOL_SESSION_PLUGIN_H_
 #define REMOTING_PROTOCOL_SESSION_PLUGIN_H_
 
 #include <memory>
 
-#include "base/callback.h"
-#include "remoting/protocol/jingle_messages.h"
-#include "remoting/protocol/session.h"
 #include "third_party/libjingle_xmpp/xmllite/xmlelement.h"
 
 namespace remoting {
 namespace protocol {
 
 // Interface for Session plugins. Plugins allow to send and receive optional
 // information that is not essential for session handshake. Messages generated
 // by the plugins on one end of a connection are attached to the session
 // handshake messages and passed to the plugins on the other end. Plugins are
 // optional, i.e. Session doesn't need any plugins to connect successfully.
 class SessionPlugin {
  public:
   SessionPlugin() = default;
   virtual ~SessionPlugin() = default;
 
   // Returns an XmlElement if the SessionPlugin requires to attach some data
   // into the outgoing message.
   virtual std::unique_ptr<buzz::XmlElement> GetNextMessage() = 0;
 
   // Handles messages in |attachments|.
   virtual void OnIncomingMessage(const buzz::XmlElement& attachments) = 0;
 };
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_SESSION_PLUGIN_H_