Use MountGuest to mount cryptohome for a demo user.

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 "base/memory/scoped_ptr.h"
 #include "chrome/browser/chromeos/app_mode/kiosk_profile_loader.h"
 
 class Profile;
 
 namespace chromeos {
 
 // Class responsible for launching the demo app under a kiosk session.
 class DemoAppLauncher : public KioskProfileLoader::Delegate {
  public:
   DemoAppLauncher();
   virtual ~DemoAppLauncher();
 
   void StartDemoAppLaunch();
 
   static bool IsDemoAppSession(const std::string& user_id);
+  static const char kDemoUserName[];
 
  private:
   // KioskProfileLoader::Delegate overrides:
   virtual void OnProfileLoaded(Profile* profile) OVERRIDE;
   virtual void OnProfileLoadFailed(KioskAppLaunchError::Error error) OVERRIDE;
 
   Profile* profile_;
   scoped_ptr<KioskProfileLoader> kiosk_profile_loader_;
 
   DISALLOW_COPY_AND_ASSIGN(DemoAppLauncher);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_DEMO_MODE_DEMO_APP_LAUNCHER_H_