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

chrome/browser/supervised_user/legacy/supervised_user_sync_service.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_SUPERVISED_USER_LEGACY_SUPERVISED_USER_SYNC_SERVICE_H_
 #define CHROME_BROWSER_SUPERVISED_USER_LEGACY_SUPERVISED_USER_SYNC_SERVICE_H_
 
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "chrome/browser/supervised_user/legacy/supervised_user_sync_service_observer.h"
 #include "chrome/browser/supervised_user/supervised_users.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/signin/core/browser/signin_manager_base.h"
 #include "sync/api/syncable_service.h"
 
 namespace base {
 class DictionaryValue;
 }
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 class PrefService;
 class Profile;
 
 class SupervisedUserSyncService : public KeyedService,
                                   public SigninManagerBase::Observer,
                                   public syncer::SyncableService {
  public:
   // For use with GetSupervisedUsersAsync() below.
   typedef base::Callback<void(const base::DictionaryValue*)>
       SupervisedUsersCallback;
@@ skipping 25 matching lines @@
                              int* avatar_index);
 
   // Given an |avatar_index|, it returns a string of the form:
   // "chrome-avatar-index:INDEX" where INDEX = |avatar_index|.
   // It is exposed for testing purposes only.
   static std::string BuildAvatarString(int avatar_index);
 
   void AddObserver(SupervisedUserSyncServiceObserver* observer);
   void RemoveObserver(SupervisedUserSyncServiceObserver* observer);
 
-  void AddSupervisedUser(const std::string& id,
+  void AddSupervisedUser(const user_manager::UserID& id,
                          const std::string& name,
                          const std::string& master_key,
                          const std::string& signature_key,
                          const std::string& encryption_key,
                          int avatar_index);
-  void UpdateSupervisedUser(const std::string& id,
+  void UpdateSupervisedUser(const user_manager::UserID& id,
                             const std::string& name,
                             const std::string& master_key,
                             const std::string& signature_key,
                             const std::string& encryption_key,
                             int avatar_index);
 
-  void DeleteSupervisedUser(const std::string& id);
+  void DeleteSupervisedUser(const user_manager::UserID& id);
 
   // Updates the supervised user avatar only if the supervised user has
   // no avatar and |avatar_index| is set to some value other than
   // |kNoAvatar|. If |avatar_index| equals |kNoAvatar| and the
   // supervised user has an avatar, it will be cleared. However,
   // to clear an avatar call the convenience method
   // |ClearSupervisedUserAvatar()|.
   // Returns true if the avatar value is changed (either updated or cleared)
   // and false otherwise.
-  bool UpdateSupervisedUserAvatarIfNeeded(const std::string& id,
+  bool UpdateSupervisedUserAvatarIfNeeded(const user_manager::UserID& id,
                                           int avatar_index);
-  void ClearSupervisedUserAvatar(const std::string& id);
+  void ClearSupervisedUserAvatar(const user_manager::UserID& id);
 
   // Returns a dictionary containing all supervised users supervised by this
   // custodian. This method should only be called once this service has started
   // syncing supervised users (i.e. has finished its initial merge of local and
   // server-side data, via MergeDataAndStartSyncing), as the stored data might
   // be outdated before that.
   const base::DictionaryValue* GetSupervisedUsers();
 
   // Calls the passed |callback| with a dictionary containing all supervised
   // users managed by this custodian.
@@ skipping 25 matching lines @@
   void GoogleSignedOut(const std::string& account_id,
                        const std::string& username) override;
 
   scoped_ptr<base::DictionaryValue> CreateDictionary(
       const std::string& name,
       const std::string& master_key,
       const std::string& signature_key,
       const std::string& encryption_key,
       int avatar_index);
 
-  void UpdateSupervisedUserImpl(const std::string& id,
+  void UpdateSupervisedUserImpl(const user_manager::UserID& id,
                                 const std::string& name,
                                 const std::string& master_key,
                                 const std::string& signature_key,
                                 const std::string& encryption_key,
                                 int avatar_index,
                                 bool add_user);
 
-  void NotifySupervisedUserAcknowledged(const std::string& supervised_user_id);
+  void NotifySupervisedUserAcknowledged(const user_manager::UserID& supervised_user_id);
   void NotifySupervisedUsersSyncingStopped();
   void NotifySupervisedUsersChanged();
 
   void DispatchCallbacks();
 
   Profile* profile_;
   PrefService* prefs_;
 
   scoped_ptr<syncer::SyncChangeProcessor> sync_processor_;
   scoped_ptr<syncer::SyncErrorFactory> error_handler_;
 
   ObserverList<SupervisedUserSyncServiceObserver> observers_;
 
   std::vector<SupervisedUsersCallback> callbacks_;
 
   DISALLOW_COPY_AND_ASSIGN(SupervisedUserSyncService);
 };
 
 #endif  // CHROME_BROWSER_SUPERVISED_USER_LEGACY_SUPERVISED_USER_SYNC_SERVICE_H_