6 files declare their use of ThemeInstallerInterface

ConfigActionsTest.php in core/modules/block/tests/src/Kernel/ConfigActionsTest.php
TestSiteClaroInstallTestScript.php in core/tests/Drupal/TestSite/TestSiteClaroInstallTestScript.php
TestSiteOliveroInstallTestScript.php in core/tests/Drupal/TestSite/TestSiteOliveroInstallTestScript.php
ThemeController.php in core/modules/system/src/Controller/ThemeController.php
ThemeExperimentalConfirmForm.php in core/modules/system/src/Form/ThemeExperimentalConfirmForm.php
ThemeInstallController.php in core/modules/system/tests/modules/nightwatch_theme_install_utility/src/Controller/ThemeInstallController.php

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