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

chrome/browser/signin/easy_unlock_screenlock_state_handler.h

Index: chrome/browser/signin/easy_unlock_screenlock_state_handler.h
diff --git a/chrome/browser/signin/easy_unlock_screenlock_state_handler.h b/chrome/browser/signin/easy_unlock_screenlock_state_handler.h
index c47dac80e695ca7aa8b18d11661710d0fb6f0130..431231c0b35e4555e84428e05d500c80a1009dde 100644
--- a/chrome/browser/signin/easy_unlock_screenlock_state_handler.h
+++ b/chrome/browser/signin/easy_unlock_screenlock_state_handler.h
@@ -10,6 +10,7 @@
 #include "base/strings/string16.h"
 #include "components/proximity_auth/screenlock_bridge.h"
 #include "components/proximity_auth/screenlock_state.h"
+#include "components/user_manager/user_id.h"
 
 class PrefService;
 
@@ -30,13 +31,13 @@ class EasyUnlockScreenlockStateHandler
                                // on a new Chromebook.
   };
 
-  // |user_email|: The email for the user associated with the profile to which
+  // |user_id|: The ID of the user associated with the profile to which
   //     this class is attached.
   // |initial_hardlock_state|: The initial hardlock state.
   // |screenlock_bridge|: The screenlock bridge used to update the screen lock
   //     state.
   EasyUnlockScreenlockStateHandler(
-      const std::string& user_email,
+      const user_manager::UserID& user_id,
       HardlockState initial_hardlock_state,
       proximity_auth::ScreenlockBridge* screenlock_bridge);
   ~EasyUnlockScreenlockStateHandler() override;
@@ -75,7 +76,7 @@ class EasyUnlockScreenlockStateHandler
   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;
 
   // Forces refresh of the Easy Unlock screenlock UI.
   void RefreshScreenlockState();
@@ -94,7 +95,7 @@ class EasyUnlockScreenlockStateHandler
   void UpdateScreenlockAuthType();
 
   proximity_auth::ScreenlockState state_;
-  std::string user_email_;
+  user_manager::UserID user_id_;
   proximity_auth::ScreenlockBridge* screenlock_bridge_;
 
   // State of hardlock.