Only generate one CNAME per PeerConnection.

webrtc/pc/mediasession.h

Index: webrtc/pc/mediasession.h
diff --git a/webrtc/pc/mediasession.h b/webrtc/pc/mediasession.h
index 98a1f070d687ec8457f3f22a8be70899d8ee5517..6bee87240f1a16e481c18e34ae1d577a51abbb3c 100644
--- a/webrtc/pc/mediasession.h
+++ b/webrtc/pc/mediasession.h
@@ -76,18 +76,21 @@ extern const char kMediaProtocolTcpDtlsSctp[];
 const int kAutoBandwidth = -1;
 const int kBufferedModeDisabled = 0;
 
+// Default CNAME for unit tests.
+const char kDefaultCname[] = "DefaultCname";

[pthatcher1, 2016/05/05 18:50:52]

Again, RtcpCname and "RTCP CNAME"

[Zhi Huang, 2016/05/06 01:36:53]

Done.

+
 struct MediaSessionOptions {
-  MediaSessionOptions() :
-      recv_audio(true),
-      recv_video(false),
-      data_channel_type(DCT_NONE),
-      is_muc(false),
-      vad_enabled(true),  // When disabled, removes all CN codecs from SDP.
-      rtcp_mux_enabled(true),
-      bundle_enabled(false),
-      video_bandwidth(kAutoBandwidth),
-      data_bandwidth(kDataMaxBandwidth) {
-  }
+  MediaSessionOptions()
+      : recv_audio(true),
+        recv_video(false),
+        data_channel_type(DCT_NONE),
+        is_muc(false),
+        vad_enabled(true),  // When disabled, removes all CN codecs from SDP.
+        rtcp_mux_enabled(true),
+        bundle_enabled(false),
+        video_bandwidth(kAutoBandwidth),
+        data_bandwidth(kDataMaxBandwidth),
+        cname(kDefaultCname) {}

[pthatcher1, 2016/05/05 18:50:51]

rtcp_cname

[Zhi Huang, 2016/05/06 01:36:53]

Done.

 
   bool has_audio() const {
     return recv_audio || HasSendMediaStream(MEDIA_TYPE_AUDIO);
@@ -133,6 +136,8 @@ struct MediaSessionOptions {
   int data_bandwidth;
   // content name ("mid") => options.
   std::map<std::string, TransportOptions> transport_options;
+  // The CNAME of the PeerConnection.

[pthatcher1, 2016/05/05 18:50:51]

I think it would be better to just remove this comment, other than reiterate
that there is one RTCP CNAME for an entire offer or answer.

[Zhi Huang, 2016/05/06 01:36:53]

Done.

+  std::string cname;
 
   struct Stream {
     Stream(MediaType type,