Cleanup: Pass std::string as const reference from testing/

testing/multiprocess_func_list.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 "multiprocess_func_list.h"
 
 #include <map>
 
 // Helper functions to maintain mapping of "test name"->test func.
 // The information is accessed via a global map.
@@ skipping 22 matching lines @@
 }  // namespace
 
 AppendMultiProcessTest::AppendMultiProcessTest(
     std::string test_name,
     TestMainFunctionPtr main_func_ptr,
     SetupFunctionPtr setup_func_ptr) {
   GetMultiprocessFuncMap()[test_name] =
       ProcessFunctions(main_func_ptr, setup_func_ptr);
 }
 
-int InvokeChildProcessTest(std::string test_name) {
+int InvokeChildProcessTest(const std::string& test_name) {
   MultiProcessTestMap& func_lookup_table = GetMultiprocessFuncMap();
   MultiProcessTestMap::iterator it = func_lookup_table.find(test_name);
   if (it != func_lookup_table.end()) {
     const ProcessFunctions& process_functions = it->second;
     if (process_functions.setup)
       (*process_functions.setup)();
     if (process_functions.main)
       return (*process_functions.main)();
   }
 
   return -1;
 }
 
 }  // namespace multi_process_function_list