7 files declare their use of AlterDecorator

AlterDecoratorTestPluginManager.php in drupal/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/AlterDecoratorTestPluginManager.php
Definition of Drupal\plugin_test\Plugin\plugin_test\AlterDecoratorTestPluginManager.
EntityManager.php in drupal/core/lib/Drupal/Core/Entity/EntityManager.php
Contains \Drupal\Core\Entity\EntityManager.
FormatterPluginManager.php in drupal/core/modules/field/lib/Drupal/field/Plugin/Type/Formatter/FormatterPluginManager.php
Definition of Drupal\field\Plugin\Type\Formatter\FormatterPluginManager..
JoinManager.php in drupal/core/modules/views/lib/Drupal/views/Plugin/Type/JoinManager.php
Definition of Drupal\views\Plugin\Type\JoinManager.
PluginManager.php in drupal/core/modules/views/lib/Drupal/views/Plugin/Type/PluginManager.php
Definition of Drupal\views\Plugin\Type\PluginManager.
WidgetPluginManager.php in drupal/core/modules/field/lib/Drupal/field/Plugin/Type/Widget/WidgetPluginManager.php
Definition of Drupal\field\Plugin\Type\Widget\WidgetPluginManager.
WizardManager.php in drupal/core/modules/views/lib/Drupal/views/Plugin/Type/WizardManager.php
Definition of Drupal\views\Plugin\Type\WizardManager.