Add MessagePipe interface. Use it in ChannelDispatcherBase.

remoting/protocol/host_video_dispatcher.cc

Index: remoting/protocol/host_video_dispatcher.cc
diff --git a/remoting/protocol/host_video_dispatcher.cc b/remoting/protocol/host_video_dispatcher.cc
index ca9b63436d493ac7fb32719b8af1e236a2628bac..6369d1bca262a8981fcef8faf72504c4472234ad 100644
--- a/remoting/protocol/host_video_dispatcher.cc
+++ b/remoting/protocol/host_video_dispatcher.cc
@@ -10,6 +10,7 @@
 #include "net/socket/stream_socket.h"
 #include "remoting/base/constants.h"
 #include "remoting/proto/video.pb.h"
+#include "remoting/protocol/message_pipe.h"
 #include "remoting/protocol/message_serialization.h"
 #include "remoting/protocol/video_feedback_stub.h"
 
@@ -22,7 +23,7 @@ HostVideoDispatcher::~HostVideoDispatcher() {}
 
 void HostVideoDispatcher::ProcessVideoPacket(scoped_ptr<VideoPacket> packet,
                                              const base::Closure& done) {
-  writer()->Write(SerializeAndFrameMessage(*packet), done);
+  message_pipe()->Send(packet.get(), done);
 }
 
 void HostVideoDispatcher::OnIncomingMessage(