Add signaling to support ICE renomination.

webrtc/pc/mediasession.cc

Index: webrtc/pc/mediasession.cc
diff --git a/webrtc/pc/mediasession.cc b/webrtc/pc/mediasession.cc
index 28da7315dd7ae831034a477f507c208ed18685b1..d849abd7882b53bbd485dc07315d75b9278f6c17 100644
--- a/webrtc/pc/mediasession.cc
+++ b/webrtc/pc/mediasession.cc
@@ -722,11 +722,13 @@ static bool IsRtxCodec(const C& codec) {
 
 static TransportOptions GetTransportOptions(const MediaSessionOptions& options,
                                             const std::string& content_name) {
+  TransportOptions transport_options;
   auto it = options.transport_options.find(content_name);
-  if (it == options.transport_options.end()) {
-    return TransportOptions();
+  if (it != options.transport_options.end()) {
+    transport_options = it->second;
   }
-  return it->second;
+  transport_options.ice_renomination = options.ice_renomination;

[skvlad, 2016/08/26 23:59:10]

Is options.ice_renomination always supposed to override
transport_options.ice_renomination? In that case, what is the reason to keep
them separate?

[honghaiz3, 2016/08/29 18:52:52]

Good point. I think that is the reason I have not chosen this approach at the
initial version (see patch 10). 
The reason to keep two ice_renomination options which look redundant is that the
transport options are keyed by the content names, and when we set the transport
options, the content names may not be available yet (for the first offer, for
example). So it is safer to set the ice_renomination in the Session Option and
copy it over to the transport option when the content name is known. 

+  return transport_options;
 }
 
 // Create a media content to be offered in a session-initiate,