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

chrome/browser/signin/easy_unlock_service_regular.h

Index: chrome/browser/signin/easy_unlock_service_regular.h
diff --git a/chrome/browser/signin/easy_unlock_service_regular.h b/chrome/browser/signin/easy_unlock_service_regular.h
index 1f4ff9d605b060a5c6d5f7bcde9b2063de153511..2458bd66ee68743d5f0b1285427ee1a846d9d680 100644
--- a/chrome/browser/signin/easy_unlock_service_regular.h
+++ b/chrome/browser/signin/easy_unlock_service_regular.h
@@ -32,6 +32,10 @@ namespace proximity_auth {
 class CryptAuthClient;
 }
 
+namespace user_manager {
+class UserID;
+}
+
 class EasyUnlockAppManager;
 class EasyUnlockToggleFlow;
 class Profile;
@@ -48,7 +52,7 @@ class EasyUnlockServiceRegular
  private:
   // 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;
@@ -60,9 +64,9 @@ class EasyUnlockServiceRegular
   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;
@@ -77,8 +81,10 @@ class EasyUnlockServiceRegular
   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;
 
+  // Returns email of the user currently associated with the service.
+  std::string GetUserEmail() const;
 
   // Callback when the controlling pref changes.
   void OnPrefsChanged();