Build WebRTC with data channel only.

webrtc/media/base/fakemediaengine.h

 /*
  *  Copyright (c) 2004 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 406 matching lines @@
   }
 
   virtual bool GetStats(VoiceMediaInfo* info) { return false; }
 
   virtual void SetRawAudioSink(
       uint32_t ssrc,
       std::unique_ptr<webrtc::AudioSinkInterface> sink) {
     sink_ = std::move(sink);
   }
 
+  virtual std::vector<webrtc::RtpSource> GetSources(uint32_t ssrc) const {
+    return std::vector<webrtc::RtpSource>();
+  }
+
  private:
   class VoiceChannelAudioSink : public AudioSource::Sink {
    public:
     explicit VoiceChannelAudioSink(AudioSource* source) : source_(source) {
       source_->SetSink(this);
     }
     virtual ~VoiceChannelAudioSink() {
       if (source_) {
         source_->SetSink(nullptr);
       }
@@ skipping 528 matching lines @@
   virtual const std::vector<DataCodec>& data_codecs() { return data_codecs_; }
 
  private:
   std::vector<FakeDataMediaChannel*> channels_;
   std::vector<DataCodec> data_codecs_;
 };
 
 }  // namespace cricket
 
 #endif  // WEBRTC_MEDIA_BASE_FAKEMEDIAENGINE_H_