Add MessagePipe interface. Use it in ChannelDispatcherBase.

remoting/protocol/client_control_dispatcher.cc

Index: remoting/protocol/client_control_dispatcher.cc
diff --git a/remoting/protocol/client_control_dispatcher.cc b/remoting/protocol/client_control_dispatcher.cc
index 6ee42564f70c9bd4c132c0badeb720704f5a21c3..776e9917faf2ab7585209ac7c82bb0c7b1a196e8 100644
--- a/remoting/protocol/client_control_dispatcher.cc
+++ b/remoting/protocol/client_control_dispatcher.cc
@@ -66,47 +66,47 @@ void ClientControlDispatcher::InjectClipboardEvent(
     const ClipboardEvent& event) {
   ControlMessage message;
   message.mutable_clipboard_event()->CopyFrom(event);
-  writer()->Write(SerializeAndFrameMessage(message), base::Closure());
+  message_pipe()->Send(&message, base::Closure());
 }
 
 void ClientControlDispatcher::NotifyClientResolution(
     const ClientResolution& resolution) {
   ControlMessage message;
   message.mutable_client_resolution()->CopyFrom(resolution);
-  writer()->Write(SerializeAndFrameMessage(message), base::Closure());
+  message_pipe()->Send(&message, base::Closure());
 }
 
 void ClientControlDispatcher::ControlVideo(const VideoControl& video_control) {
   ControlMessage message;
   message.mutable_video_control()->CopyFrom(video_control);
-  writer()->Write(SerializeAndFrameMessage(message), base::Closure());
+  message_pipe()->Send(&message, base::Closure());
 }
 
 void ClientControlDispatcher::ControlAudio(const AudioControl& audio_control) {
   ControlMessage message;
   message.mutable_audio_control()->CopyFrom(audio_control);
-  writer()->Write(SerializeAndFrameMessage(message), base::Closure());
+  message_pipe()->Send(&message, base::Closure());
 }
 
 void ClientControlDispatcher::SetCapabilities(
     const Capabilities& capabilities) {
   ControlMessage message;
   message.mutable_capabilities()->CopyFrom(capabilities);
-  writer()->Write(SerializeAndFrameMessage(message), base::Closure());
+  message_pipe()->Send(&message, base::Closure());
 }
 
 void ClientControlDispatcher::RequestPairing(
     const PairingRequest& pairing_request) {
   ControlMessage message;
   message.mutable_pairing_request()->CopyFrom(pairing_request);
-  writer()->Write(SerializeAndFrameMessage(message), base::Closure());
+  message_pipe()->Send(&message, base::Closure());
 }
 
 void ClientControlDispatcher::DeliverClientMessage(
     const ExtensionMessage& message) {
   ControlMessage control_message;
   control_message.mutable_extension_message()->CopyFrom(message);
-  writer()->Write(SerializeAndFrameMessage(control_message), base::Closure());
+  message_pipe()->Send(&control_message, base::Closure());
 }
 
 void ClientControlDispatcher::OnIncomingMessage(