Media track ID visibility at BWE level

webrtc/media/engine/webrtcvideoengine.cc

 /*
  *  Copyright (c) 2014 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 1589 matching lines @@
         }
 
         flexfec_enabled = true;
         parameters_.config.rtp.flexfec.ssrc = flexfec_ssrc;
         parameters_.config.rtp.flexfec.protected_media_ssrcs = {primary_ssrc};
       }
     }
   }
 
   parameters_.config.rtp.c_name = sp.cname;
+  parameters_.config.track_id = sp.id;
   if (rtp_extensions) {
     parameters_.config.rtp.extensions = *rtp_extensions;
   }
   parameters_.config.rtp.rtcp_mode = send_params.rtcp.reduced_size
                                          ? webrtc::RtcpMode::kReducedSize
                                          : webrtc::RtcpMode::kCompound;
   if (codec_settings) {
     bool force_encoder_allocation = false;
     SetCodec(*codec_settings, force_encoder_allocation);
   }
@@ skipping 1040 matching lines @@
     stream.temporal_layer_thresholds_bps.resize(GetDefaultVp9TemporalLayers() -
                                                 1);
   }
 
   std::vector<webrtc::VideoStream> streams;
   streams.push_back(stream);
   return streams;
 }
 
 }  // namespace cricket