Build WebRTC with data channel only.

webrtc/pc/peerconnection.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 380 matching lines @@
   return mandatory_constraints_satisfied == constraints->GetMandatory().size();
 }
 
 PeerConnection::PeerConnection(PeerConnectionFactory* factory)
     : factory_(factory),
       observer_(NULL),
       uma_observer_(NULL),
       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");
   RTC_DCHECK(signaling_thread()->IsCurrent());
   // Need to detach RTP senders/receivers from WebRtcSession,
   // since it's about to be destroyed.
   for (const auto& sender : senders_) {
     sender->internal()->Stop();
   }
   for (const auto& receiver : receivers_) {
@@ skipping 1893 matching lines @@
   }
   return event_log_->StartLogging(file, max_size_bytes);
 }
 
 void PeerConnection::StopRtcEventLog_w() {
   if (event_log_) {
     event_log_->StopLogging();
   }
 }
 }  // namespace webrtc