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

net/dns/mock_mdns_socket_factory.h

 // Copyright 2013 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.
 
 #ifndef NET_DNS_MOCK_MDNS_SOCKET_FACTORY_H_
 #define NET_DNS_MOCK_MDNS_SOCKET_FACTORY_H_
 
 #include <string>
 
 #include "net/dns/mdns_client_impl.h"
@@ skipping 40 matching lines @@
   MOCK_CONST_METHOD1(LeaveGroup, int(const IPAddressNumber& address));
 
   MOCK_METHOD1(SetMulticastInterface, int(uint32 interface_index));
   MOCK_METHOD1(SetMulticastTimeToLive, int(int ttl));
   MOCK_METHOD1(SetMulticastLoopbackMode, int(bool loopback));
 
   MOCK_METHOD1(SetDiffServCodePoint, int(DiffServCodePoint dscp));
 
   MOCK_METHOD0(DetachFromThread, void());
 
-  void SetResponsePacket(std::string response_packet);
+  void SetResponsePacket(const std::string& response_packet);
 
   int HandleRecvNow(IOBuffer* buffer, int size, IPEndPoint* address,
                     const CompletionCallback& callback);
 
   int HandleRecvLater(IOBuffer* buffer, int size, IPEndPoint* address,
                       const CompletionCallback& callback);
 
  private:
   std::string response_packet_;
   IPEndPoint local_address_;
@@ skipping 24 matching lines @@
                     ScopedVector<DatagramServerSocket>* sockets);
 
   scoped_refptr<IOBuffer> recv_buffer_;
   int recv_buffer_size_;
   CompletionCallback recv_callback_;
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_MOCK_MDNS_SOCKET_FACTORY_H_