Avoid the login screen re-layout during authentication.

Bug: b:276246832
Change-Id: I921e7a7b19e7cd655521ef312ff440dbf7494dec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4634717
Reviewed-by: Roman Sorokin <rsorokin@google.com>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Denis Kuznetsov <antrim@chromium.org>
Commit-Queue: Istvan Nagy <iscsi@google.com>
Cr-Commit-Position: refs/heads/main@{#1164759}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index fb8f80f3..e491723 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -93,6 +93,10 @@
   return authentication_stage_ != AuthenticationStage::kIdle;
 }
 
+bool LoginScreenController::IsAuthenticationCallbackExecuting() const {
+  return authentication_stage_ == AuthenticationStage::kUserCallback;
+}
+
 void LoginScreenController::AuthenticateUserWithPasswordOrPin(
     const AccountId& account_id,
     const std::string& password,