9 files declare their use of UserSession in Zircon Profile 8

AccountSwitcherTest.php in core/modules/system/src/Tests/Session/AccountSwitcherTest.php

Contains \Drupal\system\Tests\Session\AccountSwitcherTest.

BrowserTestBase.php in core/modules/simpletest/src/BrowserTestBase.php

Contains \Drupal\simpletest\BrowserTestBase.

Cookie.php in core/modules/user/src/Authentication/Provider/Cookie.php

Contains \Drupal\user\Authentication\Provider\Cookie.

FormCacheTest.php in core/modules/system/src/Tests/Form/FormCacheTest.php

Contains \Drupal\system\Tests\Form\FormCacheTest.

FunctionsTest.php in core/modules/system/src/Tests/Theme/FunctionsTest.php

Contains \Drupal\system\Tests\Theme\FunctionsTest.

InstallerTestBase.php in core/modules/simpletest/src/InstallerTestBase.php

Contains \Drupal\simpletest\InstallerTestBase.

RoleAccessCheckTest.php in core/tests/Drupal/Tests/Core/Route/RoleAccessCheckTest.php

Contains \Drupal\Tests\Core\Route\RoleAccessCheckTest.

UserSessionTest.php in core/tests/Drupal/Tests/Core/Session/UserSessionTest.php

Contains \Drupal\Tests\Core\Session\UserSessionTest.

WebTestBase.php in core/modules/simpletest/src/WebTestBase.php

Contains \Drupal\simpletest\WebTestBase.