Use std::string references instead of copying contents.

talk/app/webrtc/jsepsessiondescription.cc

 /*
  * libjingle
  * Copyright 2012 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 112 matching lines @@
 bool JsepSessionDescription::AddCandidate(
     const IceCandidateInterface* candidate) {
   if (!candidate || candidate->sdp_mline_index() < 0)
     return false;
   size_t mediasection_index = 0;
   if (!GetMediasectionIndex(candidate, &mediasection_index)) {
     return false;
   }
   if (mediasection_index >= number_of_mediasections())
     return false;
-  const std::string content_name =
+  const std::string& content_name =
       description_->contents()[mediasection_index].name;
   const cricket::TransportInfo* transport_info =
       description_->GetTransportInfoByName(content_name);
   if (!transport_info) {
     return false;
   }
 
   cricket::Candidate updated_candidate = candidate->candidate();
   if (updated_candidate.username().empty()) {
     updated_candidate.set_username(transport_info->description.ice_ufrag);
@@ skipping 54 matching lines @@
     if (!found) {
       // If the sdp_mid is presented but we can't find a match, we consider
       // this as an error.
       return false;
     }
   }
   return true;
 }
 
 }  // namespace webrtc