Build WebRTC with data channel only.

webrtc/pc/channel.cc

Index: webrtc/pc/channel.cc
diff --git a/webrtc/pc/channel.cc b/webrtc/pc/channel.cc
index f5428a43effac7a93fce554e11946c220946337c..9b8d25b0308c505240d76daa3c4dcdc7b01db758 100644
--- a/webrtc/pc/channel.cc
+++ b/webrtc/pc/channel.cc
@@ -1608,9 +1608,12 @@ bool VoiceChannel::GetStats(VoiceMediaInfo* stats) {
 
 std::vector<webrtc::RtpSource> VoiceChannel::GetSources(uint32_t ssrc) const {
   return worker_thread()->Invoke<std::vector<webrtc::RtpSource>>(
-      RTC_FROM_HERE,
-      Bind(&WebRtcVoiceMediaChannel::GetSources,
-           static_cast<WebRtcVoiceMediaChannel*>(media_channel()), ssrc));
+      RTC_FROM_HERE, Bind(&VoiceChannel::GetSources_w, this, ssrc));
+}
+
+std::vector<webrtc::RtpSource> VoiceChannel::GetSources_w(uint32_t ssrc) const {
+  RTC_DCHECK(worker_thread()->IsCurrent());
+  return media_channel()->GetSources(ssrc);
 }
 
 void VoiceChannel::StartMediaMonitor(int cms) {