12 files declare their use of ThemeManagerInterface in Zircon Profile 8

AssetResolver.php in core/lib/Drupal/Core/Asset/AssetResolver.php

Contains \Drupal\Core\Asset\AssetResolver.

BlockListBuilder.php in core/modules/block/src/BlockListBuilder.php

Contains \Drupal\block\BlockListBuilder.

BlockRepository.php in core/modules/block/src/BlockRepository.php

Contains \Drupal\block\BlockRepository.

CurrentThemeCondition.php in core/modules/system/src/Plugin/Condition/CurrentThemeCondition.php

Contains \Drupal\system\Plugin\Condition\CurrentThemeCondition.

ElementInfoManager.php in core/lib/Drupal/Core/Render/ElementInfoManager.php

Contains \Drupal\Core\Render\ElementInfoManager.

FormBuilder.php in core/lib/Drupal/Core/Form/FormBuilder.php

Contains \Drupal\Core\Form\FormBuilder.

LibraryDiscoveryCollector.php in core/lib/Drupal/Core/Asset/LibraryDiscoveryCollector.php

Contains \Drupal\Core\Asset\LibraryDiscoveryCollector.

LibraryDiscoveryParser.php in core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php

Contains \Drupal\Core\Asset\LibraryDiscoveryParser.

MenuTestController.php in core/modules/system/tests/modules/menu_test/src/Controller/MenuTestController.php

Contains \Drupal\menu_test\Controller\MenuTestController.

Renderer.php in core/lib/Drupal/Core/Render/Renderer.php

Contains \Drupal\Core\Render\Renderer.

ThemeCacheContext.php in core/lib/Drupal/Core/Cache/Context/ThemeCacheContext.php

Contains \Drupal\Core\Cache\Context\ThemeCacheContext.

TwigExtension.php in core/lib/Drupal/Core/Template/TwigExtension.php

Contains \Drupal\Core\Template\TwigExtension.