Build WebRTC with data channel only.

webrtc/pc/mediasession.cc

Index: webrtc/pc/mediasession.cc
diff --git a/webrtc/pc/mediasession.cc b/webrtc/pc/mediasession.cc
index 34ccdce7756b343d7c4ceb2cdc60aee2e1f986bf..c962cae05c10ef0f4e6f2f880747bfc707c54769 100644
--- a/webrtc/pc/mediasession.cc
+++ b/webrtc/pc/mediasession.cc
@@ -1266,6 +1266,7 @@ MediaSessionDescriptionFactory::MediaSessionDescriptionFactory(
     : secure_(SEC_DISABLED),
       add_legacy_(true),
       transport_desc_factory_(transport_desc_factory) {
+#ifdef HAVE_MEDIA
   channel_manager->GetSupportedAudioSendCodecs(&audio_send_codecs_);
   channel_manager->GetSupportedAudioReceiveCodecs(&audio_recv_codecs_);
   channel_manager->GetSupportedAudioRtpHeaderExtensions(&audio_rtp_extensions_);
@@ -1274,6 +1275,7 @@ MediaSessionDescriptionFactory::MediaSessionDescriptionFactory(
   channel_manager->GetSupportedDataCodecs(&data_codecs_);

[the sun, 2017/05/04 14:28:58]

Should this really be excluded?

[Zhi Huang, 2017/05/04 21:28:53]

This is because the |media_engine_| in channel manager in channelmanager is
nullptr. Another option would be adding nullptr checkers in these methods (if
media_engine == nullptr return;). Would that be better?

   NegotiateCodecs(audio_recv_codecs_, audio_send_codecs_,
                   &audio_sendrecv_codecs_);
+#endif
 }
 
 const AudioCodecs& MediaSessionDescriptionFactory::audio_sendrecv_codecs()