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

chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.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_EASY_UNLOCK_BOOTSTRAP_USER_CONTEXT_INITIALIZER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_EASY_UNLOCK_BOOTSTRAP_USER_CONTEXT_INITIALIZER_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_types.h"
 #include "chrome/browser/signin/easy_unlock_auth_attempt.h"
 #include "chrome/browser/signin/easy_unlock_service_observer.h"
 #include "chromeos/login/auth/user_context.h"
 #include "google_apis/gaia/gaia_oauth_client.h"
 
+namespace user_manager {
+class UserID;
+}
+
 namespace chromeos {
 
 // Performs initialization work for adding a new account via Easy bootstrap.
 // The class takes an authorization code then prepares a UserContext that
 // could be used to create a new account.
 class BootstrapUserContextInitializer final
     : public gaia::GaiaOAuthClient::Delegate,
       public EasyUnlockServiceObserver {
  public:
   // Callback type to be invoked after initialization work is done.
@@ skipping 15 matching lines @@
  private:
   void Notify(bool success);
 
   // Starts to check existing Smart lock keys to use.
   void StartCheckExistingKeys();
 
   void OnGetEasyUnlockData(bool success,
                            const EasyUnlockDeviceKeyDataList& data_list);
   void OnEasyUnlockAuthenticated(EasyUnlockAuthAttempt::Type auth_attempt_type,
                                  bool success,
-                                 const std::string& user_id,
+                                 const user_manager::UserID& user_id,
                                  const std::string& key_secret,
                                  const std::string& key_label);
   void CreateRandomKey();
 
   // Start refresh token and user info fetching.
   void StartTokenFetch(const std::string& auth_code);
 
   // gaia::GaiaOAuthClient::Delegate
   void OnGetTokensResponse(const std::string& refresh_token,
                            const std::string& access_token,
@@ skipping 17 matching lines @@
   base::WeakPtrFactory<BootstrapUserContextInitializer> weak_ptr_factory_;
 
   static CompleteCallback* complete_callback_for_testing_;
 
   DISALLOW_COPY_AND_ASSIGN(BootstrapUserContextInitializer);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_EASY_UNLOCK_BOOTSTRAP_USER_CONTEXT_INITIALIZER_H_