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

chrome/browser/ui/webui/options/supervised_user_import_handler.cc

Index: chrome/browser/ui/webui/options/supervised_user_import_handler.cc
diff --git a/chrome/browser/ui/webui/options/supervised_user_import_handler.cc b/chrome/browser/ui/webui/options/supervised_user_import_handler.cc
index 80c0470ddee504e370faa20e80d637de43daad75..c5821c0a99f2e1bba207b20662c1fe185b41fb5f 100644
--- a/chrome/browser/ui/webui/options/supervised_user_import_handler.cc
+++ b/chrome/browser/ui/webui/options/supervised_user_import_handler.cc
@@ -25,6 +25,7 @@
 #include "chrome/grit/generated_resources.h"
 #include "components/signin/core/browser/signin_error_controller.h"
 #include "components/signin/core/browser/signin_manager.h"
+#include "components/user_manager/user_id.h"
 #include "content/public/browser/web_ui.h"
 #include "grit/theme_resources.h"
 
@@ -185,7 +186,7 @@ void SupervisedUserImportHandler::SendExistingSupervisedUsers(
       g_browser_process->profile_manager()->GetProfileInfoCache();
 
   // Collect the ids of local supervised user profiles.
-  std::set<std::string> supervised_user_ids;
+  std::set<user_manager::UserID> supervised_user_ids;
   for (size_t i = 0; i < cache.GetNumberOfProfiles(); ++i) {
     if (cache.ProfileIsLegacySupervisedAtIndex(i))
       supervised_user_ids.insert(cache.GetSupervisedUserIdOfProfileAtIndex(i));
@@ -232,7 +233,7 @@ void SupervisedUserImportHandler::SendExistingSupervisedUsers(
             profiles::GetDefaultAvatarIconUrl(avatar_index);
     supervised_user->SetString("iconURL", avatar_url);
     bool on_current_device =
-        supervised_user_ids.find(it.key()) != supervised_user_ids.end();
+        supervised_user_ids.find(user_manager::UserID::FromUserEmail(it.key())) != supervised_user_ids.end();
     supervised_user->SetBoolean("onCurrentDevice", on_current_device);
 
     supervised_users.Append(supervised_user);