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

chrome/browser/ui/webui/chromeos/login/gaia_screen_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_CHROMEOS_LOGIN_GAIA_SCREEN_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_GAIA_SCREEN_HANDLER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/chromeos/login/screens/core_oobe_actor.h"
 #include "chrome/browser/extensions/signin/scoped_gaia_auth_extension.h"
 #include "chrome/browser/ui/webui/chromeos/login/base_screen_handler.h"
 #include "chrome/browser/ui/webui/chromeos/login/network_state_informer.h"
 #include "net/base/net_errors.h"
 
 namespace policy {
 class ConsumerManagementService;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 namespace chromeos {
 
 class SigninScreenHandler;
 class SigninScreenHandlerDelegate;
 
 // A class that's used to specify the way how Gaia should be loaded.
 struct GaiaContext {
   GaiaContext();
 
   // Forces Gaia to reload.
@@ skipping 106 matching lines @@
                       bool using_saml,
                       bool success);
 
   // Really handles the complete login message.
   void DoCompleteLogin(const std::string& gaia_id,
                        const std::string& typed_email,
                        const std::string& password,
                        bool using_saml);
 
   // Fill GAIA user name.
-  void PopulateEmail(const std::string& user_id);
+  void PopulateEmail(const std::string& email);
 
   // Mark user as having password changed:
-  void PasswordChangedFor(const std::string& user_id);
+  void PasswordChangedFor(const user_manager::UserID& user_id);
 
   // Kick off cookie / local storage cleanup.
   void StartClearingCookies(const base::Closure& on_clear_callback);
   void OnCookiesCleared(const base::Closure& on_clear_callback);
 
   // Kick off DNS cache flushing.
   void StartClearingDnsCache();
   void OnDnsCleared();
 
   // Show sign-in screen for the given credentials.
-  virtual void ShowSigninScreenForCreds(const std::string& username,
+  virtual void ShowSigninScreenForCreds(const user_manager::UserID& user_id,
                                         const std::string& password);
   // Attempts login for test.
   void SubmitLoginFormForTest();
 
   // Updates the member variable and UMA histogram indicating whether the
   // principals API was used during SAML login.
   void SetSAMLPrincipalsAPIUsed(bool api_used);
 
   // Show the sign-in screen. Depending on internal state, the screen will
   // either be shown immediately or after an asynchronous clean-up process that
@@ skipping 39 matching lines @@
 
   // Consumer management service for checking if enrollment is in progress.
   policy::ConsumerManagementService* consumer_management_;
 
   CoreOobeActor* core_oobe_actor_;
 
   // Email to pre-populate with.
   std::string populated_email_;
 
   // Emails of the users, whose passwords have recently been changed.
-  std::set<std::string> password_changed_for_;
+  std::set<user_manager::UserID> password_changed_for_;
 
   // True if dns cache cleanup is done.
   bool dns_cleared_;
 
   // True if DNS cache task is already running.
   bool dns_clear_task_running_;
 
   // True if cookie jar cleanup is done.
   bool cookies_cleared_;
 
@@ skipping 35 matching lines @@
   scoped_ptr<ScopedGaiaAuthExtension> auth_extension_;
 
   base::WeakPtrFactory<GaiaScreenHandler> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(GaiaScreenHandler);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_UI_WEBUI_CHROMEOS_LOGIN_GAIA_SCREEN_HANDLER_H_