We should use UserID object to identify users instead of username.

chrome/browser/chromeos/login/demo_mode/demo_app_launcher.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_LOGIN_DEMO_MODE_DEMO_APP_LAUNCHER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_DEMO_MODE_DEMO_APP_LAUNCHER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/chromeos/app_mode/kiosk_profile_loader.h"
 
 namespace base {
 class FilePath;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 namespace chromeos {
 
 // Class responsible for launching the demo app under a kiosk session.
 class DemoAppLauncher : public KioskProfileLoader::Delegate {
  public:
   DemoAppLauncher();
   ~DemoAppLauncher() override;
 
   void StartDemoAppLaunch();
 
-  static bool IsDemoAppSession(const std::string& user_id);
+  static bool IsDemoAppSession(const user_manager::UserID& user_id);
   static void SetDemoAppPathForTesting(const base::FilePath& path);
 
-  static const char kDemoUserName[];
   static const char kDemoAppId[];
 
+  static user_manager::UserID GetDemoUserID();
  private:
   friend class DemoAppLauncherTest;
 
   // KioskProfileLoader::Delegate overrides:
   void OnProfileLoaded(Profile* profile) override;
   void OnProfileLoadFailed(KioskAppLaunchError::Error error) override;
 
   scoped_ptr<KioskProfileLoader> kiosk_profile_loader_;
 
   static base::FilePath* demo_app_path_;
 
   DISALLOW_COPY_AND_ASSIGN(DemoAppLauncher);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_DEMO_MODE_DEMO_APP_LAUNCHER_H_