Revert of RTCRtpReceiver.getContributingSources() added.

chrome/test/data/webrtc/peerconnection_rtp.js

 /**
  * Copyright 2017 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 // Public interface to tests. These are expected to be called with
 // ExecuteJavascript invocations from the browser tests and will return answers
 // through the DOM automation controller.
 
@@ skipping 46 matching lines @@
   if (peerConnection_().getReceivers().length != remoteTracks.size)
     throw failTest('The number of receivers and tracks are not the same.');
 
   let receivers = new Set();
   let receiverTracks = new Set();
   peerConnection_().getReceivers().forEach(function(receiver) {
     if (receiver == null)
       throw failTest('receiver is null or undefined.');
     if (receiver.track == null)
       throw failTest('receiver.track is null or undefined.');
-    if (receiver.getContributingSources().length != 0)
-      throw failTest('receiver.getContributingSources() is not empty.');
     receivers.add(receiver);
     receiverTracks.add(receiver.track);
   });
   if (receiverTracks.size != receivers.size)
     throw failTest('receiverTracks.size != receivers.size');
 
   if (!setEquals_(receiverTracks, remoteTracks)) {
     throw failTest('The set of receiver tracks is not equal to the set of ' +
                    'stream tracks.');
   }
@@ skipping 20 matching lines @@
   if (a == null)
     return b == null;
   if (a.size != b.size)
     return false;
   a.forEach(function(value) {
     if (!b.has(value))
       return false;
   });
   return true;
 }