24 files declare their use of PluginBase

BlockBase.php in drupal/core/modules/block/lib/Drupal/block/BlockBase.php
Contains \Drupal\block\BlockBase.
CKEditorPluginBase.php in drupal/core/modules/ckeditor/lib/Drupal/ckeditor/CKEditorPluginBase.php
Contains \Drupal\ckeditor\Plugin\CKEditorPluginBase.
ContainerFactoryPluginBase.php in drupal/core/lib/Drupal/Core/Plugin/ContainerFactoryPluginBase.php
Contains \Drupal\Core\Plugin\ContainerFactoryPluginBase.
DefaultProcessor.php in drupal/core/modules/aggregator/lib/Drupal/aggregator/Plugin/aggregator/processor/DefaultProcessor.php
Contains \Drupal\aggregator\Plugin\aggregator\processor\DefaultProcessor.
Editor.php in drupal/core/modules/editor/lib/Drupal/editor/Plugin/InPlaceEditor/Editor.php
Contains \Drupal\editor\Plugin\InPlaceEditor\Editor.
EditorBase.php in drupal/core/modules/edit/lib/Drupal/edit/EditorBase.php
Contains \Drupal\edit\EditorBase.
EditorBase.php in drupal/core/modules/editor/lib/Drupal/editor/Plugin/EditorBase.php
Contains \Drupal\editor\Plugin\EditorBase.
FilterBase.php in drupal/core/modules/filter/lib/Drupal/filter/Plugin/FilterBase.php
Contains \Drupal\filter\Plugin\Filter\FilterBase.
GDToolkit.php in drupal/core/modules/system/lib/Drupal/system/Plugin/ImageToolkit/GDToolkit.php
Contains \Drupal\system\Plugin\ImageToolkit\GDToolkit;.
Llama.php in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/Llama.php
Contains \Drupal\ckeditor_test\Plugin\CKEditorPlugin\Llama.
LlamaButton.php in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/LlamaButton.php
Contains \Drupal\ckeditor_test\Plugin\CKEditorPlugin\LlamaButton.
LlamaContextual.php in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/LlamaContextual.php
Contains \Drupal\ckeditor_test\Plugin\CKEditorPlugin\LlamaContextual.
LlamaContextualAndButton.php in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/LlamaContextualAndButton.php
Contains \Drupal\ckeditor_test\Plugin\CKEditorPlugin\LlamaContextualAndButton.
MockLayoutBlock.php in drupal/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/plugin_test/mock_block/MockLayoutBlock.php
Definition of Drupal\plugin_test\Plugin\plugin_test\mock_block\MockLayoutBlock.
MockMenuBlock.php in drupal/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/plugin_test/mock_block/MockMenuBlock.php
Definition of Drupal\plugin_test\Plugin\plugin_test\mock_block\MockMenuBlock.
MockTestBlock.php in drupal/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/plugin_test/mock_block/MockTestBlock.php
Contains Drupal\plugin_test\Plugin\plugin_test\mock_block\MockTestBlock.
MockUserLoginBlock.php in drupal/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test/Plugin/plugin_test/mock_block/MockUserLoginBlock.php
Definition of Drupal\plugin_test\Plugin\plugin_test\mock_block\MockUserLoginBlock.
PluginSettingsBase.php in drupal/core/modules/field/lib/Drupal/field/Plugin/PluginSettingsBase.php
Definition of Drupal\field\Plugin\PluginSettingsBase.
PluginUIBase.php in drupal/core/modules/system/lib/Drupal/system/Plugin/PluginUIBase.php
Contains \Drupal\system\Plugin\PluginUIBase.
ResourceBase.php in drupal/core/modules/rest/lib/Drupal/rest/Plugin/ResourceBase.php
Definition of Drupal\rest\Plugin\ResourceBase.
StaticLayout.php in drupal/core/modules/layout/lib/Drupal/layout/Plugin/Layout/StaticLayout.php
Contains \Drupal\layout\Plugin\Layout\StaticLayout.
TestProcessor.php in drupal/core/modules/aggregator/tests/modules/aggregator_test/lib/Drupal/aggregator_test/Plugin/aggregator/processor/TestProcessor.php
Contains \Drupal\aggregator_test\Plugin\aggregator\processor\TestProcessor.
TestToolkit.php in drupal/core/modules/system/tests/modules/image_test/lib/Drupal/image_test/Plugin/ImageToolkit/TestToolkit.php
Contains \Drupal\image_test\Plugin\ImageToolkit\TestToolkit.
TipPluginBase.php in drupal/core/modules/tour/lib/Drupal/tour/TipPluginBase.php
Contains \Drupal\tour\TipPluginBase.