Separate out IPC::Message::Sender and channel::Listener into a separate class.

ipc/ipc_listener.h

+// Copyright (c) 2012 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 IPC_IPC_LISTENER_H_
+#define IPC_IPC_LISTENER_H_
+
+#include "base/basictypes.h"
+#include "build/build_config.h"
+#include "ipc/ipc_export.h"
+
+namespace IPC {
+
+class Message;
+
+// Implemented by consumers of a Channel to receive messages.
+class IPC_EXPORT Listener {
+ public:
+  virtual ~Listener() {}
+
+  // Called when a message is received.  Returns true iff the message was
+  // handled.
+  virtual bool OnMessageReceived(const Message& message) = 0;
+
+  // Called when the channel is connected and we have received the internal
+  // Hello message from the peer.
+  virtual void OnChannelConnected(int32 peer_pid) {}
+
+  // Called when an error is detected that causes the channel to close.
+  // This method is not called when a channel is closed normally.
+  virtual void OnChannelError() {}
+
+#if defined(OS_POSIX)
+  // Called on the server side when a channel that listens for connections
+  // denies an attempt to connect.
+  virtual void OnChannelDenied() {}
+
+  // Called on the server side when a channel that listens for connections
+  // has an error that causes the listening channel to close.
+  virtual void OnChannelListenError() {}
+#endif  // OS_POSIX
+};
+
+}  // namespace IPC
+
+#endif  // IPC_IPC_LISTENER_H_