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

chrome/browser/ui/webui/options/create_profile_handler.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_UI_WEBUI_OPTIONS_CREATE_PROFILE_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_OPTIONS_CREATE_PROFILE_HANDLER_H_
 
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_window.h"
 #include "chrome/browser/ui/host_desktop.h"
 #include "chrome/browser/ui/webui/options/options_ui.h"
 #include "google_apis/gaia/google_service_auth_error.h"
 
 
 namespace base {
 class DictionaryValue;
 class ListValue;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 #if defined(ENABLE_SUPERVISED_USERS)
 class SupervisedUserRegistrationUtility;
 #endif
 
 namespace options {
 
 // Handler for the 'create profile' overlay.
 class CreateProfileHandler: public OptionsPageUIHandler {
  public:
   CreateProfileHandler();
@@ skipping 36 matching lines @@
   //   4: a string representing the supervised user ID.
   void CreateProfile(const base::ListValue* args);
 
   // If a local error occurs during profile creation, then show an appropriate
   // error message. However, if profile creation succeeded and the
   // profile being created/imported is a supervised user profile,
   // then proceed with the registration step. Otherwise, update the UI
   // as the final task after a new profile has been created.
   void OnProfileCreated(bool create_shortcut,
                         chrome::HostDesktopType desktop_type,
-                        const std::string& supervised_user_id,
+                        const user_manager::UserID& supervised_user_id,
                         Profile* profile,
                         Profile::CreateStatus status);
 
   void HandleProfileCreationSuccess(bool create_shortcut,
                                     chrome::HostDesktopType desktop_type,
-                                    const std::string& supervised_user_id,
+                                    const user_manager::UserID& supervised_user_id,
                                     Profile* profile);
 
   // Creates desktop shortcut and updates the UI to indicate success
   // when creating a profile.
   void CreateShortcutAndShowSuccess(bool create_shortcut,
                                     chrome::HostDesktopType desktop_type,
                                     Profile* profile);
 
   // Updates the UI to show an error when creating a profile.
   void ShowProfileCreationError(Profile* profile, const base::string16& error);
@@ skipping 23 matching lines @@
 
   // Indicates the type of the in progress profile creation operation.
   // The value is only relevant while we are creating/importing a profile.
   ProfileCreationOperationType profile_creation_type_;
 
 #if defined(ENABLE_SUPERVISED_USERS)
   // Extracts the supervised user ID from the args passed into CreateProfile,
   // sets |profile_creation_type_| if necessary, and returns true if the
   // supervised user id specified in |args| are valid.
   bool ProcessSupervisedCreateProfileArgs(const base::ListValue* args,
-                                          std::string* supervised_user_id);
+                                          user_manager::UserID* supervised_user_id);
 
   // Cancels creation of a supervised-user profile currently in progress, as
   // indicated by profile_path_being_created_, removing the object and files
   // and canceling supervised-user registration. This is the handler for the
   // "cancelCreateProfile" message. |args| is not used.
   void HandleCancelProfileCreation(const base::ListValue* args);
 
   // Internal implementation. This may safely be called whether profile creation
   // or registration is in progress or not. |user_initiated| should be true if
   // the cancellation was deliberately requested by the user, and false if it
   // was caused implicitly, e.g. by shutting down the browser.
   void CancelProfileRegistration(bool user_initiated);
 
   // After a new supervised-user profile has been created, registers the user
   // with the management server.
   void RegisterSupervisedUser(bool create_shortcut,
                               chrome::HostDesktopType desktop_type,
-                              const std::string& managed_user_id,
+                              const user_manager::UserID& managed_user_id,
                               Profile* new_profile);
 
   // Called back with the result of the supervised user registration.
   void OnSupervisedUserRegistered(bool create_shortcut,
                                   chrome::HostDesktopType desktop_type,
                                   Profile* profile,
                                   const GoogleServiceAuthError& error);
 
   // Records UMA histograms relevant to supervised user profiles
   // creation and registration.
   void RecordSupervisedProfileCreationMetrics(
       GoogleServiceAuthError::State error_state);
 
   bool IsValidExistingSupervisedUserId(
-      const std::string& existing_supervised_user_id) const;
+      const user_manager::UserID& existing_supervised_user_id) const;
 
   scoped_ptr<SupervisedUserRegistrationUtility>
       supervised_user_registration_utility_;
 #endif
 
   base::WeakPtrFactory<CreateProfileHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CreateProfileHandler);
 };
 
 }  // namespace options
 
 #endif  // CHROME_BROWSER_UI_WEBUI_OPTIONS_CREATE_PROFILE_HANDLER_H_