Add the URL attribute to cricket::Candiate.

webrtc/p2p/base/turnport.cc

Index: webrtc/p2p/base/turnport.cc
diff --git a/webrtc/p2p/base/turnport.cc b/webrtc/p2p/base/turnport.cc
index 7e0e64d6edacaf97751c3cbc56d18ca9a6f88dad..34d23a4a4903f8ab93ea39404f6263b2f1d487fd 100644
--- a/webrtc/p2p/base/turnport.cc
+++ b/webrtc/p2p/base/turnport.cc
@@ -745,7 +745,7 @@ void TurnPort::OnAllocateSuccess(const rtc::SocketAddress& address,
              ProtoToString(server_address_.proto),  // The first hop protocol.
              "",  // TCP canddiate type, empty for turn candidates.
              RELAY_PORT_TYPE, GetRelayPreference(server_address_.proto),
-             server_priority_, true);
+             server_priority_, ReconstructedServerUrl(), true);
 }
 
 void TurnPort::OnAllocateError() {
@@ -1073,6 +1073,36 @@ bool TurnPort::SetEntryChannelId(const rtc::SocketAddress& address,
   return true;
 }
 
+std::string TurnPort::ReconstructedServerUrl() {
+  // draft-petithuguenin-behave-turn-uris-01
+  // turnURI       = scheme ":" turn-host [ ":" turn-port ]
+  //                 [ "?transport=" transport ]
+  // scheme        = "turn" / "turns"
+  // transport     = "udp" / "tcp" / transport-ext
+  // transport-ext = 1*unreserved
+  // turn-host     = IP-literal / IPv4address / reg-name
+  // turn-port     = *DIGIT
+  std::string scheme = "turn";
+  std::string transport = "tcp";
+  switch (server_address_.proto) {
+    case PROTO_SSLTCP:
+    case PROTO_TLS:
+      scheme = "turns";
+      break;
+    case PROTO_UDP:
+      transport = "udp";
+      break;
+    case PROTO_TCP:
+      break;
+    default:

[Taylor Brandstetter, 2017/02/10 16:59:50]

nit: Actually, you don't need the default case here. This is something I learned
recently: we have compile warnings if there is an unhandled enum in a switch
statement (-Wswitch), so by leaving out "default", you have a compile-time check
that all the enum's values are handled.

[Zhi Huang, 2017/02/10 18:57:14]

Oh I see. Good to know that! Thanks.
Done.

+      RTC_NOTREACHED() << "The protocol of the ICE server is unknown.";
+  }
+  std::ostringstream url;
+  url << scheme << ":" << server_address_.address.ipaddr().ToString() << ":"
+      << server_address_.address.port() << "?transport=" << transport;
+  return url.str();
+}
+
 TurnAllocateRequest::TurnAllocateRequest(TurnPort* port)
     : StunRequest(new TurnMessage()),
       port_(port) {