Build WebRTC with data channel only.

webrtc/pc/peerconnection.cc

Index: webrtc/pc/peerconnection.cc
diff --git a/webrtc/pc/peerconnection.cc b/webrtc/pc/peerconnection.cc
index a3981039e6cfe89554092b4c14d7f2f7b0f175e4..dc5de8707fb68f77397691a5284375901cc9a8f9 100644
--- a/webrtc/pc/peerconnection.cc
+++ b/webrtc/pc/peerconnection.cc
@@ -398,10 +398,13 @@ PeerConnection::PeerConnection(PeerConnectionFactory* factory)
       signaling_state_(kStable),
       ice_connection_state_(kIceConnectionNew),
       ice_gathering_state_(kIceGatheringNew),
+#ifdef HAVE_MEDIA
       event_log_(RtcEventLog::Create()),
+#endif

[pthatcher1, 2017/05/03 18:05:53]

We might want an RtcEventLog even if we don't have media.  How much size does it
add?

Maybe have a separate HAVE_RTC_EVENT_LOG.

[Zhi Huang, 2017/05/04 01:08:03]

With RtcEvenLog which depends on the rtc_rtcp module, the size would be ~2.77Mb.
Before adding an additional build flag, one thing I need to figure out is that
if the internal application have the control on these flag since they are not
using gn. If they don't, I think it would better to avoid adding new flags. What
do you think?

       rtcp_cname_(GenerateRtcpCname()),
       local_streams_(StreamCollection::Create()),
-      remote_streams_(StreamCollection::Create()) {}
+      remote_streams_(StreamCollection::Create()) {
+}
 
 PeerConnection::~PeerConnection() {
   TRACE_EVENT0("webrtc", "PeerConnection::~PeerConnection");