7 files declare their use of Esi

EsiFragmentRenderer.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Fragment/EsiFragmentRenderer.php
EsiFragmentRendererTest.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Tests/Fragment/EsiFragmentRendererTest.php
EsiListener.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/EventListener/EsiListener.php
EsiListenerTest.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Tests/EventListener/EsiListenerTest.php
EsiTest.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Tests/HttpCache/EsiTest.php
HttpCache.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/HttpCache/HttpCache.php
HttpCacheTestCase.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Tests/HttpCache/HttpCacheTestCase.php