Add client and host dispatchers for video_stats channel to send video stats from host to client.

remoting/base/constants.cc

 // 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.
 
 #include "remoting/base/constants.h"
 
 namespace remoting {
 
 const char kChromotingXmlNamespace[] = "google:remoting";
 
 const char kAudioChannelName[] = "audio";
 const char kControlChannelName[] = "control";
 const char kEventChannelName[] = "event";
 const char kVideoChannelName[] = "video";
+const char kVideoStatsChannelNamePrefix[] = "video_stats:";
 
 const char kMimeTypeTextUtf8[] = "text/plain; charset=UTF-8";
 
 }  // namespace remoting