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

net/dns/mock_mdns_socket_factory.cc

 // 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.
 
 #include <algorithm>
 
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
 #include "base/thread_task_runner_handle.h"
 #include "net/base/net_errors.h"
@@ skipping 18 matching lines @@
   return SendToInternal(std::string(buf->data(), buf_len), address.ToString(),
                         callback);
 }
 
 int MockMDnsDatagramServerSocket::GetLocalAddress(IPEndPoint* address) const {
   *address = local_address_;
   return OK;
 }
 
 void MockMDnsDatagramServerSocket::SetResponsePacket(
-    std::string response_packet) {
+    const std::string& response_packet) {
   response_packet_ = response_packet;
 }
 
 int MockMDnsDatagramServerSocket::HandleRecvNow(
     IOBuffer* buffer, int size, IPEndPoint* address,
     const CompletionCallback& callback) {
   int size_returned =
       std::min(response_packet_.size(), static_cast<size_t>(size));
   memcpy(buffer->data(), response_packet_.data(), size_returned);
   return size_returned;
@@ skipping 61 matching lines @@
 }
 
 int MockMDnsSocketFactory::SendToInternal(
     const std::string& packet, const std::string& address,
     const CompletionCallback& callback) {
   OnSendTo(packet);
   return packet.size();
 }
 
 }  // namespace net