Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/lib/Drupal/Component/Plugin/Derivative/DeriverBase.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Plugin\Derivative\DeriverBase.
+ */
+
+namespace Drupal\Component\Plugin\Derivative;
+
+/**
+ * Provides a basic deriver.
+ */
+abstract class DeriverBase implements DeriverInterface {
+
+  /**
+   * List of derivative definitions.
+   *
+   * @var array
+   */
+  protected $derivatives = array();
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDerivativeDefinition($derivative_id, $base_plugin_definition) {
+    if (!empty($this->derivatives) && !empty($this->derivatives[$derivative_id])) {
+      return $this->derivatives[$derivative_id];
+    }
+    $this->getDerivativeDefinitions($base_plugin_definition);
+    return $this->derivatives[$derivative_id];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDerivativeDefinitions($base_plugin_definition) {
+    return $this->derivatives;
+  }
+}

core/lib/Drupal/Component/Plugin/Derivative/DeriverInterface.php

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+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Plugin\Derivative\DeriverInterface.
+ */
+
+namespace Drupal\Component\Plugin\Derivative;
+
+/**
+ * Provides additional plugin definitions based on an existing definition.
+ *
+ * @ingroup plugin_api
+ */
+interface DeriverInterface {
+
+  /**
+   * Gets the definition of a derivative plugin.
+   *
+   * @param string $derivative_id
+   *   The derivative id. The id must uniquely identify the derivative within a
+   *   given base plugin, but derivative ids can be reused across base plugins.
+   * @param mixed $base_plugin_definition
+   *   The definition of the base plugin from which the derivative plugin
+   *   is derived. It is maybe an entire object or just some array, depending
+   *   on the discovery mechanism.
+   *
+   * @return array
+   *   The full definition array of the derivative plugin, typically a merge of
+   *   $base_plugin_definition with extra derivative-specific information. NULL
+   *   if the derivative doesn't exist.
+   */
+  public function getDerivativeDefinition($derivative_id, $base_plugin_definition);
+
+  /**
+   * Gets the definition of all derivatives of a base plugin.
+   *
+   * @param array $base_plugin_definition
+   *   The definition array of the base plugin.
+   * @return array
+   *   An array of full derivative definitions keyed on derivative id.
+   *
+   * @see getDerivativeDefinition()
+   */
+  public function getDerivativeDefinitions($base_plugin_definition);
+
+}