Change the default rtcp mux policy from negotiate to require.

third_party/WebKit/Source/modules/peerconnection/RTCPeerConnection.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 243 matching lines @@
   WebRTCBundlePolicy bundlePolicy = WebRTCBundlePolicy::kBalanced;
   String bundlePolicyString = configuration.bundlePolicy();
   if (bundlePolicyString == "max-compat") {
     bundlePolicy = WebRTCBundlePolicy::kMaxCompat;
   } else if (bundlePolicyString == "max-bundle") {
     bundlePolicy = WebRTCBundlePolicy::kMaxBundle;
   } else {
     DCHECK_EQ(bundlePolicyString, "balanced");
   }
 
   // For the histogram value of "WebRTC.PeerConnection.SelectedRtcpMuxPolicy".

[foolip, 2016/11/29 10:24:42]

This histogram exists only to gauge the risk of this change I think. Can you
remove it in this CL too?

[zhihuang1, 2016/11/29 22:47:24]

Done.

   *selectedRtcpMuxPolicy = RtcpMuxPolicyDefault;
-  WebRTCRtcpMuxPolicy rtcpMuxPolicy = WebRTCRtcpMuxPolicy::kNegotiate;
+  WebRTCRtcpMuxPolicy rtcpMuxPolicy = WebRTCRtcpMuxPolicy::kRequire;
   if (configuration.hasRtcpMuxPolicy()) {
     String rtcpMuxPolicyString = configuration.rtcpMuxPolicy();
     if (rtcpMuxPolicyString == "require") {
       *selectedRtcpMuxPolicy = RtcpMuxPolicyRequire;
-      rtcpMuxPolicy = WebRTCRtcpMuxPolicy::kRequire;
     } else {
       DCHECK_EQ(rtcpMuxPolicyString, "negotiate");
+      rtcpMuxPolicy = WebRTCRtcpMuxPolicy::kNegotiate;
       *selectedRtcpMuxPolicy = RtcpMuxPolicyNegotiate;
     }
   }
 
   WebRTCConfiguration webConfiguration;
   webConfiguration.iceTransportPolicy = iceTransportPolicy;
   webConfiguration.bundlePolicy = bundlePolicy;
   webConfiguration.rtcpMuxPolicy = rtcpMuxPolicy;
 
   if (configuration.hasIceServers()) {
@@ skipping 1197 matching lines @@
 DEFINE_TRACE(RTCPeerConnection) {
   visitor->trace(m_localStreams);
   visitor->trace(m_remoteStreams);
   visitor->trace(m_dispatchScheduledEventRunner);
   visitor->trace(m_scheduledEvents);
   EventTargetWithInlineData::trace(visitor);
   ActiveDOMObject::trace(visitor);
 }
 
 }  // namespace blink