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..9e56d67d38860fe11da087ecdee2d2ef3cc1f027 100644
--- a/webrtc/pc/channel.cc
+++ b/webrtc/pc/channel.cc
@@ -30,6 +30,10 @@
 namespace cricket {
 using rtc::Bind;
 
+std::vector<webrtc::RtpSource> GetSourcesImpl(
+    WebRtcVoiceMediaChannel* media_channel,
+    uint32_t ssrc);
+
 namespace {
 // See comment below for why we need to use a pointer to a unique_ptr.
 bool SetRawAudioSink_w(VoiceMediaChannel* channel,
@@ -1608,9 +1612,13 @@ 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 GetSourcesImpl(static_cast<WebRtcVoiceMediaChannel*>(media_channel()),

[Taylor Brandstetter, 2017/05/18 17:57:05]

This wouldn't be necessary if GetSources was pure virtual, which I think it
should have been in the first place.

[Zhi Huang, 2017/05/23 03:40:35]

Yes. Once the circular dependency problem is solved. we can call the method
without downcasting.

+                        ssrc);
 }
 
 void VoiceChannel::StartMediaMonitor(int cms) {