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

chrome/browser/signin/easy_unlock_service_signin_chromeos.h

Index: chrome/browser/signin/easy_unlock_service_signin_chromeos.h
diff --git a/chrome/browser/signin/easy_unlock_service_signin_chromeos.h b/chrome/browser/signin/easy_unlock_service_signin_chromeos.h
index 634de98d5bac2ec2007c02345c4011674d89b2a8..76c0bd521c19345a55429b536ccf873b7bbc8902 100644
--- a/chrome/browser/signin/easy_unlock_service_signin_chromeos.h
+++ b/chrome/browser/signin/easy_unlock_service_signin_chromeos.h
@@ -17,6 +17,7 @@
 #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
@@ -29,7 +30,7 @@ class EasyUnlockServiceSignin
 
   // 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.
@@ -63,7 +64,7 @@ class EasyUnlockServiceSignin
 
   // 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;
@@ -75,9 +76,9 @@ class EasyUnlockServiceSignin
   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;
@@ -92,7 +93,7 @@ class EasyUnlockServiceSignin
   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;
@@ -103,7 +104,7 @@ class EasyUnlockServiceSignin
 
   // 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);
 
@@ -112,10 +113,10 @@ class EasyUnlockServiceSignin
   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