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

chrome/browser/ui/ash/system_tray_delegate_chromeos_browsertest_chromeos.cc

 // Copyright 2014 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/ui/ash/system_tray_delegate_chromeos.h"
 
 #include <string>
 
 #include "ash/display/display_manager.h"
 #include "ash/shell.h"
@@ skipping 65 matching lines @@
   }
 };
 
 class SystemTrayDelegateChromeOSTest : public LoginManagerTest {
  protected:
   SystemTrayDelegateChromeOSTest()
       : LoginManagerTest(false /* should_launch_browser */) {}
 
   ~SystemTrayDelegateChromeOSTest() override {}
 
-  void SetupUserProfile(std::string user_name, bool use_24_hour_clock) {
+  void SetupUserProfile(const std::string& user_name, bool use_24_hour_clock) {
     const user_manager::User* user =
         user_manager::UserManager::Get()->FindUser(user_name);
     Profile* profile = ProfileHelper::Get()->GetProfileByUser(user);
     profile->GetPrefs()->SetBoolean(prefs::kUse24HourClock, use_24_hour_clock);
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SystemTrayDelegateChromeOSTest);
 };
 
@@ skipping 50 matching lines @@
 
   UpdateDisplay("400x400");
 
   ui_test_utils::NavigateToURL(browser(), GURL("chrome://version"));
   UpdateDisplay("400x400/r");
   // Ensure that there is a notification that is shown.
   EXPECT_FALSE(GetVisibleNotifications().empty());
 }
 
 }  // namespace chromeos