Adding the ability to create an RtpSender without a track.

talk/app/webrtc/peerconnectioninterface.h

 /*
  * 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 319 matching lines @@
   // Note that a SessionDescription negotiation is need before the
   // remote peer is notified.
   virtual void RemoveStream(MediaStreamInterface* stream) = 0;
 
   // Returns pointer to the created DtmfSender on success.
   // Otherwise returns NULL.
   virtual rtc::scoped_refptr<DtmfSenderInterface> CreateDtmfSender(
       AudioTrackInterface* track) = 0;
 
   // TODO(deadbeef): Make these pure virtual once all subclasses implement them.
+  // |kind| must be "audio" or "video".

[pthatcher1, 2015/10/20 17:42:49]

I think we could use cricket::MediaType here and say it must be MEDIA_TYPE_AUDIO
or MEDIA_TYPE_VIDEO.

[Taylor Brandstetter, 2015/10/21 00:22:08]

Done.

+  virtual rtc::scoped_refptr<RtpSenderInterface> CreateSender(
+      const std::string& kind) {
+    return rtc::scoped_refptr<RtpSenderInterface>();
+  }
+
   virtual std::vector<rtc::scoped_refptr<RtpSenderInterface>> GetSenders()
       const {
     return std::vector<rtc::scoped_refptr<RtpSenderInterface>>();
   }
 
   virtual std::vector<rtc::scoped_refptr<RtpReceiverInterface>> GetReceivers()
       const {
     return std::vector<rtc::scoped_refptr<RtpReceiverInterface>>();
   }
 
@@ skipping 287 matching lines @@
 CreatePeerConnectionFactory(
     rtc::Thread* worker_thread,
     rtc::Thread* signaling_thread,
     AudioDeviceModule* default_adm,
     cricket::WebRtcVideoEncoderFactory* encoder_factory,
     cricket::WebRtcVideoDecoderFactory* decoder_factory);
 
 }  // namespace webrtc
 
 #endif  // TALK_APP_WEBRTC_PEERCONNECTIONINTERFACE_H_