10 files declare their use of HandlerBase

AreaPluginBase.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/area/AreaPluginBase.php
Definition of Drupal\views\Plugin\views\area\AreaPluginBase.
ArgumentPluginBase.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/argument/ArgumentPluginBase.php
Definition of Drupal\views\Plugin\views\argument\ArgumentPluginBase.
FieldPluginBase.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/field/FieldPluginBase.php
Definition of Drupal\views\Plugin\views\field\FieldPluginBase.
FilterPluginBase.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/filter/FilterPluginBase.php
Definition of Drupal\views\Plugin\views\filter\FilterPluginBase.
HandlerAllTest.php in drupal/core/modules/views/lib/Drupal/views/Tests/Handler/HandlerAllTest.php
Definition of Drupal\views\Tests\Handler\HandlerAllTest.
HandlerTest.php in drupal/core/modules/views/lib/Drupal/views/Tests/Handler/HandlerTest.php
Definition of Drupal\views\Tests\Handler\HandlerTest.
ManyToOneHelper.php in drupal/core/modules/views/lib/Drupal/views/ManyToOneHelper.php
Definition of Drupal\views\ManyToOneHelper.
RelationshipPluginBase.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/relationship/RelationshipPluginBase.php
Definition of Drupal\views\Plugin\views\relationship\RelationshipPluginBase.
SortPluginBase.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/sort/SortPluginBase.php
Definition of Drupal\views\Plugin\views\sort\SortPluginBase.
Sql.php in drupal/core/modules/views/lib/Drupal/views/Plugin/views/query/Sql.php
Definition of Drupal\views\Plugin\views\query\Sql.