Use std::string references instead of copying contents.

talk/session/media/mediasession.cc

Index: talk/session/media/mediasession.cc
diff --git a/talk/session/media/mediasession.cc b/talk/session/media/mediasession.cc
index dc4f4080afc4bbcec5d24e5a8ffae6d57730dcaa..8d07e95a150d8a53e0190fd4f909d8b188b85137 100644
--- a/talk/session/media/mediasession.cc
+++ b/talk/session/media/mediasession.cc
@@ -529,7 +529,7 @@ static bool UpdateTransportInfoForBundle(const ContentGroup& bundle_group,
   }
 
   // We should definitely have a transport for the first content.
-  std::string selected_content_name = *bundle_group.FirstContentName();
+  const std::string& selected_content_name = *bundle_group.FirstContentName();
   const TransportInfo* selected_transport_info =
       sdesc->GetTransportInfoByName(selected_content_name);
   if (!selected_transport_info) {
@@ -537,9 +537,9 @@ static bool UpdateTransportInfoForBundle(const ContentGroup& bundle_group,
   }
 
   // Set the other contents to use the same ICE credentials.
-  const std::string selected_ufrag =
+  const std::string& selected_ufrag =
       selected_transport_info->description.ice_ufrag;
-  const std::string selected_pwd =
+  const std::string& selected_pwd =
       selected_transport_info->description.ice_pwd;
   for (TransportInfos::iterator it =
            sdesc->transport_infos().begin();