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

chrome/browser/chromeos/login/supervised/supervised_user_creation_controller_new.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_SUPERVISED_SUPERVISED_USER_CREATION_CONTROLLER_NEW_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SUPERVISED_SUPERVISED_USER_CREATION_CONTROLLER_NEW_H_
 
 #include <string>
 
 #include "base/files/file_path.h"
@@ skipping 23 matching lines @@
 // 7. Mark "transaction" as completed.
 // 8. End manager session.
 class SupervisedUserCreationControllerNew
     : public SupervisedUserCreationController,
       public ExtendedAuthenticator::NewAuthStatusConsumer {
  public:
   // All UI initialization is deferred till Init() call.
   // |Consumer| is not owned by controller, and it is expected that it wouldn't
   // be deleted before SupervisedUserCreationControllerNew.
   SupervisedUserCreationControllerNew(StatusConsumer* consumer,
-                                      const std::string& manager_id);
+                                      const user_manager::UserID& manager_id);
   ~SupervisedUserCreationControllerNew() override;
 
   // Returns the current supervised user controller if it has been created.
   static SupervisedUserCreationControllerNew* current_controller() {
     return current_controller_;
   }
 
   // Set up controller for creating new supervised user with |display_name|,
   // |password| and avatar indexed by |avatar_index|. StartCreation() have to
   // be called to actually start creating user.
@@ skipping 23 matching lines @@
                    const std::string& master_key,
                    const base::DictionaryValue* password_data,
                    const std::string& encryption_key,
                    const std::string& signature_key) override;
 
   void SetManagerProfile(Profile* manager_profile) override;
   Profile* GetManagerProfile() override;
 
   void CancelCreation() override;
   void FinishCreation() override;
-  std::string GetSupervisedUserId() override;
+  const user_manager::UserID& GetSupervisedUserId() const override;
 
  private:
   enum Stage {
     // Just initial stage.
     STAGE_INITIAL,
 
     // Creation attempt is recoreded to allow cleanup in case of failure.
     TRANSACTION_STARTED,
     // Different keys are generated and public ones are stored in LocalState.
     KEYS_GENERATED,
@@ skipping 13 matching lines @@
   enum CreationType { NEW_USER, USER_IMPORT_OLD, USER_IMPORT_NEW, };
 
   // Contains information necessary for new user creation.
   struct UserCreationContext {
     UserCreationContext();
     ~UserCreationContext();
 
     base::string16 display_name;
     int avatar_index;
 
-    std::string manager_id;
+    user_manager::UserID manager_id;
 
-    std::string local_user_id;  // Used to identify cryptohome.
+    user_manager::UserID local_user_id;  // Used to identify cryptohome.
     std::string sync_user_id;   // Used to identify user in manager's sync data.
 
     // Keys:
     std::string master_key;       // Random string
     std::string signature_key;    // 256 bit HMAC key
     std::string encryption_key;   // 256 bit HMAC key
     std::string salted_password;  // Hash(salt + Hash(password))
 
     std::string password;
 
@@ skipping 48 matching lines @@
 
   // Factory of callbacks.
   base::WeakPtrFactory<SupervisedUserCreationControllerNew> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SupervisedUserCreationControllerNew);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SUPERVISED_SUPERVISED_USER_CREATION_CONTROLLER_NEW_H_