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

chrome/browser/signin/easy_unlock_service_signin_chromeos.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_SIGNIN_EASY_UNLOCK_SERVICE_SIGNIN_CHROMEOS_H_
 #define CHROME_BROWSER_SIGNIN_EASY_UNLOCK_SERVICE_SIGNIN_CHROMEOS_H_
 
 #include <map>
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "chrome/browser/chromeos/login/easy_unlock/easy_unlock_types.h"
 #include "chrome/browser/signin/easy_unlock_service.h"
 #include "chromeos/login/login_state.h"
 #include "components/proximity_auth/screenlock_bridge.h"
+#include "components/user_manager/user_id.h"
 
 // EasyUnlockService instance that should be used for signin profile.
 class EasyUnlockServiceSignin
     : public EasyUnlockService,
       public proximity_auth::ScreenlockBridge::Observer,
       public chromeos::LoginState::Observer {
  public:
   explicit EasyUnlockServiceSignin(Profile* profile);
   ~EasyUnlockServiceSignin() override;
 
   // Sets |user_id| as the current user of the service. Note this does
   // not change the focused user on the login screen.
-  void SetCurrentUser(const std::string& user_id);
+  void SetCurrentUser(const user_manager::UserID& user_id);
 
  private:
   // The load state of a user's cryptohome key data.
   enum UserDataState {
     // Initial state, the key data is empty and not being loaded.
     USER_DATA_STATE_INITIAL,
     // The key data is empty, but being loaded.
     USER_DATA_STATE_LOADING,
     // The key data has been loaded.
     USER_DATA_STATE_LOADED
@@ skipping 13 matching lines @@
     // The list of remote device dictionaries understood by Easy unlock app.
     // This will be returned by |GetRemoteDevices| method.
     base::ListValue remote_devices_value;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(UserData);
   };
 
   // EasyUnlockService implementation:
   EasyUnlockService::Type GetType() const override;
-  std::string GetUserEmail() const override;
+  user_manager::UserID GetUserID() const override;
   void LaunchSetup() override;
   const base::DictionaryValue* GetPermitAccess() const override;
   void SetPermitAccess(const base::DictionaryValue& permit) override;
   void ClearPermitAccess() override;
   const base::ListValue* GetRemoteDevices() const override;
   void SetRemoteDevices(const base::ListValue& devices) override;
   void RunTurnOffFlow() override;
   void ResetTurnOffFlow() override;
   TurnOffFlowStatus GetTurnOffFlowStatus() const override;
   std::string GetChallenge() const override;
   std::string GetWrappedSecret() const override;
-  void RecordEasySignInOutcome(const std::string& user_id,
+  void RecordEasySignInOutcome(const user_manager::UserID& user_id,
                                bool success) const override;
-  void RecordPasswordLoginEvent(const std::string& user_id) const override;
+  void RecordPasswordLoginEvent(const user_manager::UserID& user_id) const override;
   void StartAutoPairing(const AutoPairingResultCallback& callback) override;
   void SetAutoPairingResult(bool success, const std::string& error) override;
   void InitializeInternal() override;
   void ShutdownInternal() override;
   bool IsAllowedInternal() const override;
   void OnWillFinalizeUnlock(bool success) override;
   void OnSuspendDone() override;
 
   // proximity_auth::ScreenlockBridge::Observer implementation:
   void OnScreenDidLock(proximity_auth::ScreenlockBridge::LockHandler::ScreenType
                            screen_type) override;
   void OnScreenDidUnlock(
       proximity_auth::ScreenlockBridge::LockHandler::ScreenType screen_type)
       override;
-  void OnFocusedUserChanged(const std::string& user_id) override;
+  void OnFocusedUserChanged(const user_manager::UserID& user_id) override;
 
   // chromeos::LoginState::Observer implementation:
   void LoggedInStateChanged() override;
 
   // Loads the device data associated with the user's Easy unlock keys from
   // crypthome.
   void LoadCurrentUserDataIfNeeded();
 
   // Callback invoked when the user's device data is loaded from cryptohome.
   void OnUserDataLoaded(
-      const std::string& user_id,
+      const user_manager::UserID& user_id,
       bool success,
       const chromeos::EasyUnlockDeviceKeyDataList& data);
 
   // If the device data has been loaded for the current user, returns it.
   // Otherwise, returns NULL.
   const UserData* FindLoadedDataForCurrentUser() const;
 
   // User id of the user currently associated with the service.
-  std::string user_id_;
+  user_manager::UserID user_id_;
 
   // Maps user ids to their fetched cryptohome key data.
-  std::map<std::string, UserData*> user_data_;
+  std::map<user_manager::UserID, UserData*> user_data_;
 
   // Whether failed attempts to load user data should be retried.
   // This is to handle case where cryptohome daemon is not started in time the
   // service attempts to load some data. Retries will be allowed only until the
   // first data load finishes (even if it fails).
   bool allow_cryptohome_backoff_;
 
   // Whether the service has been successfully initialized, and has not been
   // shut down.
   bool service_active_;
 
   // The timestamp for the most recent time when a user pod was focused.
   base::TimeTicks user_pod_last_focused_timestamp_;
 
   base::WeakPtrFactory<EasyUnlockServiceSignin> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(EasyUnlockServiceSignin);
 };
 
 #endif  // CHROME_BROWSER_SIGNIN_EASY_UNLOCK_SERVICE_SIGNIN_CHROMEOS_H_