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

chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.h

Index: chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.h
diff --git a/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.h b/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.h
index c2ea90f3b1f5c1c1127379be03bbeea6d6546998..e0f880dc7ed70eb61d3856320552ab029793e3ee 100644
--- a/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.h
+++ b/chrome/browser/chromeos/login/easy_unlock/bootstrap_user_context_initializer.h
@@ -17,6 +17,10 @@
 #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.
@@ -52,7 +56,7 @@ class BootstrapUserContextInitializer final
                            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();