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

chrome/browser/chromeos/app_mode/kiosk_app_data.h

 // Copyright 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_APP_MODE_KIOSK_APP_DATA_H_
 #define CHROME_BROWSER_CHROMEOS_APP_MODE_KIOSK_APP_DATA_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/extensions/webstore_data_fetcher_delegate.h"
+#include "components/user_manager/user_id.h"
 #include "ui/gfx/image/image_skia.h"
 #include "url/gurl.h"
 
 class Profile;
 
 namespace extensions {
 class Extension;
 class WebstoreDataFetcher;
 }
 
@@ skipping 16 matching lines @@
  public:
   enum Status {
     STATUS_INIT,     // Data initialized with app id.
     STATUS_LOADING,  // Loading data from cache or web store.
     STATUS_LOADED,   // Data loaded.
     STATUS_ERROR,    // Failed to load data.
   };
 
   KioskAppData(KioskAppDataDelegate* delegate,
                const std::string& app_id,
-               const std::string& user_id,
+               const user_manager::UserID& user_id,
                const GURL& update_url);
   ~KioskAppData() override;
 
   // Loads app data from cache. If there is no cached data, fetches it
   // from web store.
   void Load();
 
   // Clears locally cached data.
   void ClearCache();
 
   // Loads app data from the app installed in the given profile.
   void LoadFromInstalledApp(Profile* profile, const extensions::Extension* app);
 
   // Sets full path of the cache crx. The crx would be used to extract meta
   // data for private apps.
   void SetCachedCrx(const base::FilePath& crx_file);
 
   // Returns true if web store data fetching is in progress.
   bool IsLoading() const;
 
   // Returns true if the update url points to Webstore.
   bool IsFromWebStore() const;
 
   const std::string& app_id() const { return app_id_; }
-  const std::string& user_id() const { return user_id_; }
+  const user_manager::UserID& user_id() const { return user_id_; }
   const std::string& name() const { return name_; }
   const GURL& update_url() const { return update_url_; }
   const gfx::ImageSkia& icon() const { return icon_; }
   Status status() const { return status_; }
 
  private:
   class CrxLoader;
   class IconLoader;
   class WebstoreDataParser;
 
@@ skipping 41 matching lines @@
   // Extracts meta data from crx file when loading from Webstore and local
   // cache fails.
   void MaybeLoadFromCrx();
 
   void OnCrxLoadFinished(const CrxLoader* crx_loader);
 
   KioskAppDataDelegate* delegate_;  // not owned.
   Status status_;
 
   std::string app_id_;
-  std::string user_id_;
+  user_manager::UserID user_id_;
   std::string name_;
   GURL update_url_;
   gfx::ImageSkia icon_;
 
   scoped_ptr<extensions::WebstoreDataFetcher> webstore_fetcher_;
   base::FilePath icon_path_;
 
   base::FilePath crx_file_;
 
   DISALLOW_COPY_AND_ASSIGN(KioskAppData);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_APP_MODE_KIOSK_APP_DATA_H_