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

chrome/browser/chromeos/login/kiosk_browsertest.cc

 // Copyright (c) 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 <vector>
 
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/desktop_background/desktop_background_controller_observer.h"
 #include "ash/shell.h"
 #include "base/bind.h"
@@ skipping 180 matching lines @@
 void OnNetworkWaitTimedOut(const base::Closure& runner_quit_task) {
   runner_quit_task.Run();
 }
 
 // Helper function for LockFileThread.
 void LockAndUnlock(scoped_ptr<base::Lock> lock) {
   lock->Acquire();
   lock->Release();
 }
 
-bool IsAppInstalled(const std::string app_id) {
+bool IsAppInstalled(const std::string& app_id) {
   Profile* app_profile = ProfileManager::GetPrimaryUserProfile();
   DCHECK(app_profile);
   const extensions::Extension* app =
       extensions::ExtensionSystem::Get(app_profile)
           ->extension_service()
           ->GetInstalledExtension(app_id);
   return app != nullptr;
 }
 
 // Helper functions for CanConfigureNetwork mock.
@@ skipping 1134 matching lines @@
     KioskAppManager::Get()->UpdateExternalCache();
     waiter.Wait();
     EXPECT_TRUE(waiter.loaded());
     std::string cached_version;
     base::FilePath file_path;
     EXPECT_TRUE(
         manager->GetCachedCrx(test_app_id(), &file_path, &cached_version));
     EXPECT_EQ(version, cached_version);
   }
 
-  void SetupFakeDiskMountManagerMountPath(const std::string mount_path) {
+  void SetupFakeDiskMountManagerMountPath(const std::string& mount_path) {
     base::FilePath test_data_dir;
     PathService::Get(chrome::DIR_TEST_DATA, &test_data_dir);
     test_data_dir = test_data_dir.AppendASCII(mount_path);
     fake_disk_mount_manager_->set_usb_mount_path(test_data_dir.value());
   }
 
   void SimulateUpdateAppFromUsbStick(const std::string& usb_mount_path,
                                      bool* app_update_notified,
                                      bool* update_success) {
     SetupFakeDiskMountManagerMountPath(usb_mount_path);
@@ skipping 743 matching lines @@
   content::WindowedNotificationObserver(
       chrome::NOTIFICATION_KIOSK_AUTOLAUNCH_WARNING_VISIBLE,
       content::NotificationService::AllSources()).Wait();
 
   // Wait for the wallpaper to load.
   WaitForWallpaper();
   EXPECT_TRUE(wallpaper_loaded());
 }
 
 }  // namespace chromeos