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()),

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

fyi: there's a RtcEventLog::CreateNull() to use so there is no need to check
event_log_ at every deref...

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

The idea here is to remove the dependency on the target "rtc_event_log_impl". So
I don't think we can call CreateNull() which requires the implementation detail.
But we can move all the implementation details (the impl of StartLogging()) of
the RtcEventLogNullImpl from .cc to the header (so that we can depend on the
interface only) and then call "new RtcEventLogNullImpl()" here. What do you
think?

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