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

chrome/utility/importer/firefox_importer_unittest_utils_mac.cc

 // 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.
 
 #include "chrome/utility/importer/firefox_importer_unittest_utils.h"
 
 #include "base/base_switches.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
@@ skipping 227 matching lines @@
 
   void SetSender(IPC::Sender* sender) {
     sender_ = sender;
   }
 
   void OnDecryptor_Init(base::FilePath dll_path, base::FilePath db_path) {
     bool ret = decryptor_.Init(dll_path, db_path);
     sender_->Send(new Msg_Decryptor_InitReturnCode(ret));
   }
 
-  void OnDecrypt(std::string crypt) {
+  void OnDecrypt(const std::string& crypt) {
     base::string16 unencrypted_str = decryptor_.Decrypt(crypt);
     sender_->Send(new Msg_Decryptor_Response(unencrypted_str));
   }
 
   void OnParseSignons(base::FilePath signons_path) {
     std::vector<autofill::PasswordForm> forms;
     decryptor_.ReadAndParseSignons(signons_path, &forms);
     sender_->Send(new Msg_ParseSignons_Response(forms));
   }
 
@@ skipping 28 matching lines @@
   scoped_ptr<IPC::Channel> channel = IPC::Channel::CreateClient(
       kTestChannelID, &listener);
   CHECK(channel->Connect());
   listener.SetSender(channel.get());
 
   // run message loop
   base::MessageLoop::current()->Run();
 
   return 0;
 }