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

chrome/browser/signin/chrome_signin_client.cc

Index: chrome/browser/signin/chrome_signin_client.cc
diff --git a/chrome/browser/signin/chrome_signin_client.cc b/chrome/browser/signin/chrome_signin_client.cc
index cc4aed9dbfa6c2b27d9fda82358337ebe26ace7a..063a652853afdf862a9c7e149d28aac494e132f4 100644
--- a/chrome/browser/signin/chrome_signin_client.cc
+++ b/chrome/browser/signin/chrome_signin_client.cc
@@ -62,7 +62,7 @@ ChromeSigninClient::ChromeSigninClient(
   if (!user)
     return;
   auto* user_manager = user_manager::UserManager::Get();
-  const std::string& user_id = user->GetUserID();
+  const user_manager::UserID& user_id = user->GetUserID();
   if (user_manager->GetKnownUserDeviceId(user_id).empty()) {
     const std::string legacy_device_id =
         GetPrefs()->GetString(prefs::kGoogleServicesSigninScopedDeviceId);