Reland of Adding the ability to create an RtpSender without a track.

talk/app/webrtc/webrtcsession.cc

 /*
  * libjingle
  * Copyright 2012 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 1721 matching lines @@
   return true;
 }
 
 void WebRtcSession::RemoveUnusedChannels(const SessionDescription* desc) {
   // Destroy video_channel_ first since it may have a pointer to the
   // voice_channel_.
   const cricket::ContentInfo* video_info =
       cricket::GetFirstVideoContent(desc);
   if ((!video_info || video_info->rejected) && video_channel_) {
     SignalVideoChannelDestroyed();
-    const std::string content_name = video_channel_->content_name();
     channel_manager_->DestroyVideoChannel(video_channel_.release());
   }
 
   const cricket::ContentInfo* voice_info =
       cricket::GetFirstAudioContent(desc);
   if ((!voice_info || voice_info->rejected) && voice_channel_) {
     SignalVoiceChannelDestroyed();
-    const std::string content_name = voice_channel_->content_name();
     channel_manager_->DestroyVoiceChannel(voice_channel_.release());
   }
 
   const cricket::ContentInfo* data_info =
       cricket::GetFirstDataContent(desc);
   if ((!data_info || data_info->rejected) && data_channel_) {
     SignalDataChannelDestroyed();
-    const std::string content_name = data_channel_->content_name();
     channel_manager_->DestroyDataChannel(data_channel_.release());
   }
 }
 
 // TODO(mallinath) - Add a correct error code if the channels are not created
 // due to BUNDLE is enabled but rtcp-mux is disabled.
 bool WebRtcSession::CreateChannels(const SessionDescription* desc) {
   // Creating the media channels and transport proxies.
   const cricket::ContentInfo* voice = cricket::GetFirstAudioContent(desc);
   if (voice && !voice->rejected && !voice_channel_) {
@@ skipping 420 matching lines @@
   }
 }
 
 void WebRtcSession::OnSentPacket_w(cricket::TransportChannel* channel,
                                    const rtc::SentPacket& sent_packet) {
   RTC_DCHECK(worker_thread()->IsCurrent());
   media_controller_->call_w()->OnSentPacket(sent_packet);
 }
 
 }  // namespace webrtc