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

chrome/browser/chromeos/login/users/supervised_user_manager.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_USERS_SUPERVISED_USER_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_USERS_SUPERVISED_USER_MANAGER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/strings/string16.h"
 #include "base/values.h"
 #include "chrome/browser/profiles/profile.h"
 
 class PrefRegistrySimple;
 
 namespace user_manager {
 class User;
+class UserID;
 }
 
 namespace chromeos {
 
 class SupervisedUserAuthentication;
 
 // Keys in dictionary with supervised password information.
 extern const char kSchemaVersion[];
 extern const char kPasswordRevision[];
 extern const char kSalt[];
@@ skipping 18 matching lines @@
       LoadTokenCallback;
 
   // Registers user manager preferences.
   static void RegisterPrefs(PrefRegistrySimple* registry);
 
   SupervisedUserManager() {}
   virtual ~SupervisedUserManager() {}
 
   // Checks if given user have supervised users on this device.
 
-  virtual bool HasSupervisedUsers(const std::string& manager_id) const = 0;
+  virtual bool HasSupervisedUsers(const user_manager::UserID& manager_id) const = 0;
 
   // Creates supervised user with given |display_name| and |local_user_id|
   // and persists that to user list. Also links this user identified by
   // |sync_user_id| to manager with a |manager_id|.
   // Returns created user, or existing user if there already
   // was a supervised user with such display name.
   // TODO(antrim): Refactor into a single struct to have only 1 getter.
   virtual const user_manager::User* CreateUserRecord(
-      const std::string& manager_id,
-      const std::string& local_user_id,
+      const user_manager::UserID& manager_id,
+      const user_manager::UserID& local_user_id,
       const std::string& sync_user_id,
       const base::string16& display_name) = 0;
 
   // Generates unique user ID for supervised user.
-  virtual std::string GenerateUserId() = 0;
+  virtual user_manager::UserID GenerateUserId() = 0;
 
   // Returns the supervised user with the given |display_name| if found in
   // the persistent list. Returns |NULL| otherwise.
   virtual const user_manager::User* FindByDisplayName(
       const base::string16& display_name) const = 0;
 
   // Returns the supervised user with the given |sync_id| if found in
   // the persistent list. Returns |NULL| otherwise.
   virtual const user_manager::User* FindBySyncId(
       const std::string& sync_id) const = 0;
 
   // Returns sync_user_id for supervised user with |user_id| or empty string if
   // such user is not found or it doesn't have user_id defined.
-  virtual std::string GetUserSyncId(const std::string& user_id) const = 0;
+  virtual std::string GetUserSyncId(const user_manager::UserID& user_id) const = 0;
 
   // Returns the display name for manager of user |user_id| if it is known
   // (was previously set by a |SaveUserDisplayName| call).
   // Otherwise, returns a manager id.
   virtual base::string16 GetManagerDisplayName(
-      const std::string& user_id) const = 0;
+      const user_manager::UserID& user_id) const = 0;
 
   // Returns the user id for manager of user |user_id| if it is known (user is
   // actually a managed user).
   // Otherwise, returns an empty string.
-  virtual std::string GetManagerUserId(const std::string& user_id) const = 0;
+  virtual user_manager::UserID GetManagerUserId(const user_manager::UserID& user_id) const = 0;
 
   // Returns the display email for manager of user |user_id| if it is known
   // (user is actually a managed user).
   // Otherwise, returns an empty string.
-  virtual std::string GetManagerDisplayEmail(const std::string& user_id)
+  virtual std::string GetManagerDisplayEmail(const user_manager::UserID& user_id)
       const = 0;
 
   // Create a record about starting supervised user creation transaction.
   virtual void StartCreationTransaction(const base::string16& display_name) = 0;
 
   // Add user id to supervised user creation transaction record.
-  virtual void SetCreationTransactionUserId(const std::string& user_id) = 0;
+  virtual void SetCreationTransactionUserId(const user_manager::UserID& user_id) = 0;
 
   // Remove supervised user creation transaction record.
   virtual void CommitCreationTransaction() = 0;
 
   // Return object that handles specifics of supervised user authentication.
   virtual SupervisedUserAuthentication* GetAuthentication() = 0;
 
   // Fill |result| with public password-specific data for |user_id| from Local
   // State.
-  virtual void GetPasswordInformation(const std::string& user_id,
+  virtual void GetPasswordInformation(const user_manager::UserID& user_id,
                                       base::DictionaryValue* result) = 0;
 
   // Stores public password-specific data from |password_info| for |user_id| in
   // Local State.
   virtual void SetPasswordInformation(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       const base::DictionaryValue* password_info) = 0;
 
   // Loads a sync oauth token in background, and passes it to callback.
   virtual void LoadSupervisedUserToken(Profile* profile,
                                        const LoadTokenCallback& callback) = 0;
 
   // Configures sync service with oauth token.
   virtual void ConfigureSyncWithToken(Profile* profile,
                                       const std::string& token) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SupervisedUserManager);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_USERS_SUPERVISED_USER_MANAGER_H_