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

chrome/browser/supervised_user/chromeos/supervised_user_password_service.cc

Index: chrome/browser/supervised_user/chromeos/supervised_user_password_service.cc
diff --git a/chrome/browser/supervised_user/chromeos/supervised_user_password_service.cc b/chrome/browser/supervised_user/chromeos/supervised_user_password_service.cc
index 530bfab509b598faf1c22aee5d1e100fd31ebc67..50e21d7562796073f2838c8e876b5c425fd172a2 100644
--- a/chrome/browser/supervised_user/chromeos/supervised_user_password_service.cc
+++ b/chrome/browser/supervised_user/chromeos/supervised_user_password_service.cc
@@ -11,16 +11,17 @@
 #include "chrome/browser/chromeos/login/users/supervised_user_manager.h"
 #include "chrome/browser/supervised_user/legacy/supervised_user_sync_service.h"
 #include "chrome/browser/supervised_user/supervised_user_constants.h"
+#include "components/user_manager/user_id.h"
 
 namespace chromeos {
 
 SupervisedUserPasswordService::SupervisedUserPasswordService()
-    : weak_ptr_factory_(this) {}
+    : user_id_(std::string(), std::string()), weak_ptr_factory_(this) {}
 
 SupervisedUserPasswordService::~SupervisedUserPasswordService() {}
 
 void SupervisedUserPasswordService::Init(
-    const std::string& user_id,
+    const user_manager::UserID& user_id,
     SupervisedUserSharedSettingsService* shared_settings_service) {
   user_id_ = user_id;
   settings_service_ = shared_settings_service;
@@ -49,8 +50,8 @@ void SupervisedUserPasswordService::OnSharedSettingsChange(
     LOG(WARNING) << "Got notification for user not on device.";
     return;
   }
-  DCHECK(user_id_ == user->email());
-  if (user_id_ != user->email())
+  DCHECK(user_id_ == user->GetUserID());
+  if (user_id_ != user->GetUserID())
     return;
   const base::Value* value = settings_service_->GetValue(su_id, key);
   if (value == NULL) {