Change the default rtcp mux policy from negotiate to require.

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

Index: third_party/WebKit/Source/modules/peerconnection/RTCPeerConnection.cpp
diff --git a/third_party/WebKit/Source/modules/peerconnection/RTCPeerConnection.cpp b/third_party/WebKit/Source/modules/peerconnection/RTCPeerConnection.cpp
index c58565ae8451b22e0c1cf7e6c2920d0058897b31..f978ad7ce9f2b43059b20dc6f2d61884f53a0c18 100644
--- a/third_party/WebKit/Source/modules/peerconnection/RTCPeerConnection.cpp
+++ b/third_party/WebKit/Source/modules/peerconnection/RTCPeerConnection.cpp
@@ -263,14 +263,14 @@ WebRTCConfiguration parseConfiguration(ExecutionContext* context,
 
   // 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;
     }
   }