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

chromeos/login/auth/online_attempt_host.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 CHROMEOS_LOGIN_AUTH_ONLINE_ATTEMPT_HOST_H_
 #define CHROMEOS_LOGIN_AUTH_ONLINE_ATTEMPT_HOST_H_
 
 #include <string>
 
 #include "base/memory/ref_counted.h"
@@ skipping 17 matching lines @@
 class AuthAttemptState;
 class OnlineAttempt;
 class UserContext;
 
 // Helper class which hosts OnlineAttempt for online credentials checking.
 class CHROMEOS_EXPORT OnlineAttemptHost : public AuthAttemptStateResolver {
  public:
   class Delegate {
    public:
     // Called after user_context were checked online.
-    virtual void OnChecked(const std::string& username, bool success) = 0;
+    virtual void OnChecked(const user_manager::UserID& user_id, bool success) = 0;
   };
 
   explicit OnlineAttemptHost(Delegate* delegate);
   ~OnlineAttemptHost() override;
 
   // Performs an online check of the credentials in |request_context| and
   // invokes
   // the delegate's OnChecked() with the result. Note that only one check can be
   // in progress at any given time. If this method is invoked with a different
   // |user_context| than a check currently in progress, the current check will
@@ skipping 18 matching lines @@
   scoped_ptr<OnlineAttempt> online_attempt_;
   scoped_ptr<AuthAttemptState> state_;
   base::WeakPtrFactory<OnlineAttemptHost> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(OnlineAttemptHost);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROMEOS_LOGIN_AUTH_ONLINE_ATTEMPT_HOST_H_