Set the preferred DSCP value for Rtp data channel to be DSCP_AF41.

webrtc/api/webrtcsession.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 1702 matching lines @@
     quic_data_transport_->SetTransport(transport_name);
     return true;
   }
 #endif  // HAVE_QUIC
   bool sctp = (data_channel_type_ == cricket::DCT_SCTP);
   bool require_rtcp_mux =
       rtcp_mux_policy_ == PeerConnectionInterface::kRtcpMuxPolicyRequire;
   bool create_rtcp_transport_channel = !sctp && !require_rtcp_mux;
   data_channel_.reset(channel_manager_->CreateDataChannel(
       transport_controller_.get(), content->name, bundle_transport,
-      create_rtcp_transport_channel, data_channel_type_));
+      create_rtcp_transport_channel, data_channel_type_, media_controller_));

[pthatcher1, 2016/12/06 00:06:01]

This should be after transport_controller_.get() but before content->name.

   if (!data_channel_) {
     return false;
   }
   if (require_rtcp_mux) {
     data_channel_->ActivateRtcpMux();
   }
 
   if (sctp) {
     data_channel_->SignalDataReceived.connect(
         this, &WebRtcSession::OnDataChannelMessageReceived);
@@ skipping 345 matching lines @@
 }
 
 void WebRtcSession::OnDtlsHandshakeError(rtc::SSLHandshakeError error) {
   if (metrics_observer_) {
     metrics_observer_->IncrementEnumCounter(
         webrtc::kEnumCounterDtlsHandshakeError, static_cast<int>(error),
         static_cast<int>(rtc::SSLHandshakeError::MAX_VALUE));
   }
 }
 }  // namespace webrtc