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

chrome/browser/chromeos/login/session/user_session_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_SESSION_USER_SESSION_MANAGER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SESSION_USER_SESSION_MANAGER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 17 matching lines @@
 class PrefRegistrySimple;
 class PrefService;
 class Profile;
 
 namespace net {
 class URLRequestContextGetter;
 }
 
 namespace user_manager {
 class User;
+class UserID;
 }  // namespace user_manager
 
 namespace chromeos {
 
 namespace test {
 class UserSessionManagerTestApi;
 }  // namespace test
 
 class EasyUnlockKeyManager;
 class InputEventsBlocker;
@@ skipping 192 matching lines @@
 
   const UserContext& user_context() const { return user_context_; }
   bool has_auth_cookies() const { return has_auth_cookies_; }
 
   void Shutdown();
 
  private:
   friend class test::UserSessionManagerTestApi;
   friend struct DefaultSingletonTraits<UserSessionManager>;
 
-  typedef std::set<std::string> SigninSessionRestoreStateSet;
+  typedef std::set<user_manager::UserID> SigninSessionRestoreStateSet;
 
   UserSessionManager();
   ~UserSessionManager() override;
 
   // OAuth2LoginManager::Observer overrides:
   void OnSessionRestoreStateChanged(
       Profile* user_profile,
       OAuth2LoginManager::SessionRestoreState state) override;
 
   // net::NetworkChangeNotifier::ConnectionTypeObserver overrides:
@@ skipping 31 matching lines @@
   // Initializes basic preferences for newly created profile. Any other
   // early profile initialization that needs to happen before
   // ProfileManager::DoFinalInit() gets called is done here.
   void InitProfilePreferences(Profile* profile,
                               const UserContext& user_context);
 
   // Callback for Profile::CREATE_STATUS_INITIALIZED profile state.
   // Profile is created, extensions and promo resources are initialized.
   void UserProfileInitialized(Profile* profile,
                               bool is_incognito_profile,
-                              const std::string& user_id);
+                              const user_manager::UserID& user_id);
 
   // Callback to resume profile creation after transferring auth data from
   // the authentication profile.
   void CompleteProfileCreateAfterAuthTransfer(Profile* profile);
 
   // Finalized profile preparation.
   void FinalizePrepareProfile(Profile* profile);
 
   // Starts out-of-box flow with the specified screen.
   void ActivateWizard(const std::string& screen_name);
@@ skipping 30 matching lines @@
   void RestorePendingUserSessions();
 
   // Notifies observers that user pending sessions restore has finished.
   void NotifyPendingUserSessionsRestoreFinished();
 
   // Attempts restarting the browser process and esures that this does
   // not happen while we are still fetching new OAuth refresh tokens.
   void AttemptRestart(Profile* profile);
 
   // Callback invoked when Easy unlock key operations are finished.
-  void OnEasyUnlockKeyOpsFinished(const std::string& user_id,
+  void OnEasyUnlockKeyOpsFinished(const user_manager::UserID& user_id,
                                   bool success);
 
   // Internal implementation of DoBrowserLaunch. Initially should be called with
   // |locale_pref_checked| set to false which will result in postponing browser
   // launch till user locale is applied if needed. After locale check has
   // completed this method is called with |locale_pref_checked| set to true.
   void DoBrowserLaunchInternal(Profile* profile,
                                LoginDisplayHost* login_host,
                                bool locale_pref_checked);
 
@@ skipping 102 matching lines @@
   bool waiting_for_child_account_status_;
 
   base::WeakPtrFactory<UserSessionManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UserSessionManager);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SESSION_USER_SESSION_MANAGER_H_