6 files declare their use of DefinitionDecorator in Zircon Profile 8

DefinitionDecoratorTest.php in vendor/symfony/dependency-injection/Tests/DefinitionDecoratorTest.php

ResolveDefinitionTemplatesPass.php in vendor/symfony/dependency-injection/Compiler/ResolveDefinitionTemplatesPass.php

ResolveDefinitionTemplatesPassTest.php in vendor/symfony/dependency-injection/Tests/Compiler/ResolveDefinitionTemplatesPassTest.php

XmlFileLoader.php in vendor/symfony/dependency-injection/Loader/XmlFileLoader.php

YamlFileLoader.php in vendor/symfony/dependency-injection/Loader/YamlFileLoader.php

YamlFileLoader.php in core/lib/Drupal/Core/DependencyInjection/YamlFileLoader.php

Contains \Drupal\Core\DependencyInjection\YamlFileLoader.