Cleanup: Pass std::string as const reference if possible

net/tools/quic/quic_server_session.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // A server specific QuicSession subclass.
 
 #ifndef NET_TOOLS_QUIC_QUIC_SERVER_SESSION_H_
 #define NET_TOOLS_QUIC_QUIC_SERVER_SESSION_H_
 
 #include <set>
@@ skipping 73 matching lines @@
     return GetCryptoStream()->use_stateless_rejects_if_peer_supported();
   }
 
   bool PeerSupportsStatelessRejects() {
     if (GetCryptoStream() == nullptr) {
       return false;
     }
     return GetCryptoStream()->peer_supports_stateless_rejects();
   }
 
-  void set_serving_region(std::string serving_region) {
+  void set_serving_region(const std::string& serving_region) {
     serving_region_ = serving_region;
   }
 
   void set_use_stateless_rejects_if_peer_supported(
       bool use_stateless_rejects_if_peer_supported) {
     DCHECK(GetCryptoStream() != nullptr);
     GetCryptoStream()->set_use_stateless_rejects_if_peer_supported(
         use_stateless_rejects_if_peer_supported);
   }
 
@@ skipping 34 matching lines @@
   // Number of packets sent to the peer, at the time we last sent a SCUP.
   int64 last_scup_packet_number_;
 
   DISALLOW_COPY_AND_ASSIGN(QuicServerSession);
 };
 
 }  // namespace tools
 }  // namespace net
 
 #endif  // NET_TOOLS_QUIC_QUIC_SERVER_SESSION_H_