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

chrome/browser/sync/test/integration/sessions_helper.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/browser/sync/test/integration/sessions_helper.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 410 matching lines @@
 
 }  //  namespace
 
 bool AwaitCheckForeignSessionsAgainst(
     int index, const std::vector<ScopedWindowMap>& windows) {
   CheckForeignSessionsChecker checker(index, windows);
   checker.Wait();
   return !checker.TimedOut();
 }
 
-void DeleteForeignSession(int index, std::string session_tag) {
+void DeleteForeignSession(int index, const std::string& session_tag) {
   ProfileSyncServiceFactory::GetInstance()->GetForProfile(
       test()->GetProfile(index))->
           GetOpenTabsUIDelegate()->DeleteForeignSession(session_tag);
 }
 
 }  // namespace sessions_helper