Change the default rtcp mux policy from negotiate to require.

third_party/WebKit/public/platform/WebRTCConfiguration.h

 /*
  * 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 40 matching lines @@
 enum class WebRTCIceTransportPolicy { kNone, kRelay, kAll };
 
 enum class WebRTCBundlePolicy { kBalanced, kMaxCompat, kMaxBundle };
 
 enum class WebRTCRtcpMuxPolicy { kNegotiate, kRequire };
 
 struct WebRTCConfiguration {
   WebVector<WebRTCIceServer> iceServers;
   WebRTCIceTransportPolicy iceTransportPolicy = WebRTCIceTransportPolicy::kAll;
   WebRTCBundlePolicy bundlePolicy = WebRTCBundlePolicy::kBalanced;
-  WebRTCRtcpMuxPolicy rtcpMuxPolicy = WebRTCRtcpMuxPolicy::kNegotiate;
+  WebRTCRtcpMuxPolicy rtcpMuxPolicy = WebRTCRtcpMuxPolicy::kRequire;
   WebVector<std::unique_ptr<WebRTCCertificate>> certificates;
 };
 
 }  // namespace blink
 
 #endif  // WebRTCConfiguration_h