[Chromoting] Implement HostExperimentSessionPlugin

remoting/protocol/session_plugin.h

Index: remoting/protocol/session_plugin.h
diff --git a/remoting/protocol/session_plugin.h b/remoting/protocol/session_plugin.h
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+++ b/remoting/protocol/session_plugin.h
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+// 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/webrtc/libjingle/xmllite/xmlelement.h"
+
+namespace remoting {
+namespace protocol {
+
+// An interface to attach data on an outgoing message or handle an incoming of
+// message. The plugin data are designed to be optional, so this class won't
+// impact a session generation.
+class SessionPlugin {
+ public:
+  SessionPlugin(const base::Callback<std::unique_ptr<buzz::XmlElement>()>&
+                    new_attachments);
+  virtual ~SessionPlugin();
+
+  // Attachs messages in |attachments|. |state| is the current session state.
+  // |action| is the current ActionType in message.
+  virtual void OnSending(Session::State state,
+                         JingleMessage::ActionType action,
+                         std::unique_ptr<buzz::XmlElement>* attachments) = 0;
+
+  // Handles messages in |attachments|. |state| is the last session state.
+  // |action| is the current ActionType in message.
+  virtual void OnReceiving(
+      Session::State state,
+      JingleMessage::ActionType action,
+      const std::unique_ptr<buzz::XmlElement>& attachments) = 0;
+
+ protected:
+  // Creates a new "attachments" xml element.
+  const base::Callback<std::unique_ptr<buzz::XmlElement>()> new_attachments_;
+};
+
+}  // namespace protocol
+}  // namespace remoting
+
+#endif  // REMOTING_PROTOCOL_SESSION_PLUGIN_H_