diff --git a/core/lib/Drupal/Component/Plugin/PluginManagerBase.php b/core/lib/Drupal/Component/Plugin/PluginManagerBase.php
index b063627..83d3790 100644
--- a/core/lib/Drupal/Component/Plugin/PluginManagerBase.php
+++ b/core/lib/Drupal/Component/Plugin/PluginManagerBase.php
@@ -32,13 +32,6 @@
   protected $factory;
 
   /**
-   * The object that returns the preconfigured plugin instance appropriate for a particular runtime condition.
-   *
-   * @var \Drupal\Component\Plugin\Mapper\MapperInterface
-   */
-  protected $mapper;
-
-  /**
    * {@inheritdoc}
    */
   public function getDefinition($plugin_id, $exception_on_invalid = TRUE) {
@@ -72,11 +65,4 @@ public function createInstance($plugin_id, array $configuration = array()) {
     }
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getInstance(array $options) {
-    return $this->mapper->getInstance($options);
-  }
-
 }
diff --git a/core/lib/Drupal/Component/Plugin/PluginManagerInterface.php b/core/lib/Drupal/Component/Plugin/PluginManagerInterface.php
index 803682a..8a46834 100644
--- a/core/lib/Drupal/Component/Plugin/PluginManagerInterface.php
+++ b/core/lib/Drupal/Component/Plugin/PluginManagerInterface.php
@@ -8,7 +8,6 @@
 
 use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
 use Drupal\Component\Plugin\Factory\FactoryInterface;
-use Drupal\Component\Plugin\Mapper\MapperInterface;
 
 /**
  * Interface implemented by plugin managers.
@@ -29,5 +28,5 @@
  *
  * @ingroup plugin_api
  */
-interface PluginManagerInterface extends DiscoveryInterface, FactoryInterface, MapperInterface {
+interface PluginManagerInterface extends DiscoveryInterface, FactoryInterface {
 }
diff --git a/core/lib/Drupal/Core/Entity/EntityReferenceSelection/SelectionPluginManagerInterface.php b/core/lib/Drupal/Core/Entity/EntityReferenceSelection/SelectionPluginManagerInterface.php
index 278e3c4..4a3d062 100644
--- a/core/lib/Drupal/Core/Entity/EntityReferenceSelection/SelectionPluginManagerInterface.php
+++ b/core/lib/Drupal/Core/Entity/EntityReferenceSelection/SelectionPluginManagerInterface.php
@@ -53,4 +53,17 @@ public function getSelectionGroups($entity_type_id);
    */
   public function getSelectionHandler(FieldDefinitionInterface $field_definition, EntityInterface $entity = NULL);
 
+  /**
+   * Returns a preconfigured selector instance.
+   *
+   * @param array $options
+   *   Keys are:
+   *   - target_type (required): the ID of the entity type that is referenced.
+   *   - handler (optional): The ID of the selector to use.
+   *
+   * @return \Drupal\Core\Entity\EntityReferenceSelection\SelectionInterface|false
+   *   If no instance can be retrieved, FALSE will be returned.
+   */
+  public function getInstance(array $options);
+
 }
diff --git a/core/lib/Drupal/Core/Field/FormatterPluginManager.php b/core/lib/Drupal/Core/Field/FormatterPluginManager.php
index e6054a9..49638c9 100644
--- a/core/lib/Drupal/Core/Field/FormatterPluginManager.php
+++ b/core/lib/Drupal/Core/Field/FormatterPluginManager.php
@@ -17,7 +17,7 @@
  *
  * @ingroup field_formatter
  */
-class FormatterPluginManager extends DefaultPluginManager {
+class FormatterPluginManager extends DefaultPluginManager implements FormatterPluginManagerInterface {
 
   /**
    * An array of formatter options for each field type.
@@ -73,30 +73,7 @@ public function createInstance($plugin_id, array $configuration = array()) {
   }
 
   /**
-   * Overrides PluginManagerBase::getInstance().
-   *
-   * @param array $options
-   *   An array with the following key/value pairs:
-   *   - field_definition: (FieldDefinitionInterface) The field definition.
-   *   - view_mode: (string) The view mode.
-   *   - prepare: (bool, optional) Whether default values should get merged in
-   *     the 'configuration' array. Defaults to TRUE.
-   *   - configuration: (array) the configuration for the formatter. The
-   *     following key value pairs are allowed, and are all optional if
-   *     'prepare' is TRUE:
-   *     - label: (string) Position of the label. The default 'field' theme
-   *       implementation supports the values 'inline', 'above' and 'hidden'.
-   *       Defaults to 'above'.
-   *     - type: (string) The formatter to use. Defaults to the
-   *       'default_formatter' for the field type, The default formatter will
-   *       also be used if the requested formatter is not available.
-   *     - settings: (array) Settings specific to the formatter. Each setting
-   *       defaults to the default value specified in the formatter definition.
-   *     - third_party_settings: (array) Settings provided by other extensions
-   *       through hook_field_formatter_third_party_settings_form().
-   *
-   * @return \Drupal\Core\Field\FormatterInterface|null
-   *   A formatter object or NULL when plugin is not found.
+   * {@inheritdoc}
    */
   public function getInstance(array $options) {
     $configuration = $options['configuration'];
@@ -119,7 +96,7 @@ public function getInstance(array $options) {
       // Grab the default widget for the field type.
       $field_type_definition = $this->fieldTypeManager->getDefinition($field_type);
       if (empty($field_type_definition['default_formatter'])) {
-        return NULL;
+        return FALSE;
       }
       $plugin_id = $field_type_definition['default_formatter'];
     }
diff --git a/core/lib/Drupal/Core/Field/FormatterPluginManagerInterface.php b/core/lib/Drupal/Core/Field/FormatterPluginManagerInterface.php
new file mode 100644
index 0000000..5276238
--- /dev/null
+++ b/core/lib/Drupal/Core/Field/FormatterPluginManagerInterface.php
@@ -0,0 +1,47 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Field\FormatterPluginManagerInterface.
+ */
+
+namespace Drupal\Core\Field;
+
+use Drupal\Component\Plugin\PluginManagerInterface;
+
+/**
+ * Defines a field formatter plugin manager.
+ *
+ * @ingroup field_formatter
+ */
+interface FormatterPluginManagerInterface extends PluginManagerInterface {
+
+  /**
+   * Returns a preconfigured formatter.
+   *
+   * @param array $options
+   *   An array with the following key/value pairs:
+   *   - field_definition: (FieldDefinitionInterface) The field definition.
+   *   - view_mode: (string) The view mode.
+   *   - prepare: (bool, optional) Whether default values should get merged in
+   *     the 'configuration' array. Defaults to TRUE.
+   *   - configuration: (array) the configuration for the formatter. The
+   *     following key value pairs are allowed, and are all optional if
+   *     'prepare' is TRUE:
+   *     - label: (string) Position of the label. The default 'field' theme
+   *       implementation supports the values 'inline', 'above' and 'hidden'.
+   *       Defaults to 'above'.
+   *     - type: (string) The formatter to use. Defaults to the
+   *       'default_formatter' for the field type, The default formatter will
+   *       also be used if the requested formatter is not available.
+   *     - settings: (array) Settings specific to the formatter. Each setting
+   *       defaults to the default value specified in the formatter definition.
+   *     - third_party_settings: (array) Settings provided by other extensions
+   *       through hook_field_formatter_third_party_settings_form().
+   *
+   * @return \Drupal\Core\Field\FormatterInterface|null
+   *   A formatter object or NULL when plugin is not found.
+   */
+  public function getInstance(array $options);
+
+}
diff --git a/core/lib/Drupal/Core/Field/WidgetPluginManager.php b/core/lib/Drupal/Core/Field/WidgetPluginManager.php
index c251135..12b5c08 100644
--- a/core/lib/Drupal/Core/Field/WidgetPluginManager.php
+++ b/core/lib/Drupal/Core/Field/WidgetPluginManager.php
@@ -17,7 +17,7 @@
  *
  * @ingroup field_widget
  */
-class WidgetPluginManager extends DefaultPluginManager {
+class WidgetPluginManager extends DefaultPluginManager implements WidgetPluginManagerInterface {
 
   /**
    * The field type manager to define field.
@@ -55,27 +55,7 @@ public function __construct(\Traversable $namespaces, CacheBackendInterface $cac
   }
 
   /**
-   * Overrides PluginManagerBase::getInstance().
-   *
-   * @param array $options
-   *   An array with the following key/value pairs:
-   *   - field_definition: (FieldDefinitionInterface) The field definition.
-   *   - form_mode: (string) The form mode.
-   *   - prepare: (bool, optional) Whether default values should get merged in
-   *     the 'configuration' array. Defaults to TRUE.
-   *   - configuration: (array) the configuration for the widget. The
-   *     following key value pairs are allowed, and are all optional if
-   *     'prepare' is TRUE:
-   *     - type: (string) The widget to use. Defaults to the
-   *       'default_widget' for the field type. The default widget will also be
-   *       used if the requested widget is not available.
-   *     - settings: (array) Settings specific to the widget. Each setting
-   *       defaults to the default value specified in the widget definition.
-   *     - third_party_settings: (array) Settings provided by other extensions
-   *       through hook_field_formatter_third_party_settings_form().
-   *
-   * @return \Drupal\Core\Field\WidgetInterface|null
-   *   A Widget object or NULL when plugin is not found.
+   * {@inheritdoc}
    */
   public function getInstance(array $options) {
     // Fill in defaults for missing properties.
diff --git a/core/lib/Drupal/Core/Field/WidgetPluginManagerInterface.php b/core/lib/Drupal/Core/Field/WidgetPluginManagerInterface.php
new file mode 100644
index 0000000..2fb92f2
--- /dev/null
+++ b/core/lib/Drupal/Core/Field/WidgetPluginManagerInterface.php
@@ -0,0 +1,43 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Field\WidgetPluginManagerInterface.
+ */
+
+namespace Drupal\Core\Field;
+
+use Drupal\Component\Plugin\PluginManagerInterface;
+
+/**
+ * Defines a field widget plugin manager.
+ *
+ * @ingroup field_widget
+ */
+interface WidgetPluginManagerInterface extends PluginManagerInterface {
+
+  /**
+   * Returns a preconfigured widget.
+   *
+   * @param array $options
+   *   An array with the following key/value pairs:
+   *   - field_definition: (FieldDefinitionInterface) The field definition.
+   *   - form_mode: (string) The form mode.
+   *   - prepare: (bool, optional) Whether default values should get merged in
+   *     the 'configuration' array. Defaults to TRUE.
+   *   - configuration: (array) the configuration for the widget. The
+   *     following key value pairs are allowed, and are all optional if
+   *     'prepare' is TRUE:
+   *     - type: (string) The widget to use. Defaults to the
+   *       'default_widget' for the field type. The default widget will also be
+   *       used if the requested widget is not available.
+   *     - settings: (array) Settings specific to the widget. Each setting
+   *       defaults to the default value specified in the widget definition.
+   *     - third_party_settings: (array) Settings provided by other extensions
+   *       through hook_field_formatter_third_party_settings_form().
+   *
+   * @return \Drupal\Core\Field\WidgetInterface|null
+   *   A Widget object or NULL when plugin is not found.
+   */
+  public function getInstance(array $options);
+}
diff --git a/core/lib/Drupal/Core/Mail/MailManager.php b/core/lib/Drupal/Core/Mail/MailManager.php
index 1e7bdc6..c2a6197 100644
--- a/core/lib/Drupal/Core/Mail/MailManager.php
+++ b/core/lib/Drupal/Core/Mail/MailManager.php
@@ -74,58 +74,7 @@ public function __construct(\Traversable $namespaces, CacheBackendInterface $cac
   }
 
   /**
-   * Overrides PluginManagerBase::getInstance().
-   *
-   * Returns an instance of the mail plugin to use for a given message ID.
-   *
-   * The selection of a particular implementation is controlled via the config
-   * 'system.mail.interface', which is a keyed array.  The default
-   * implementation is the mail plugin whose ID is the value of 'default' key. A
-   * more specific match first to key and then to module will be used in
-   * preference to the default. To specify a different plugin for all mail sent
-   * by one module, set the plugin ID as the value for the key corresponding to
-   * the module name. To specify a plugin for a particular message sent by one
-   * module, set the plugin ID as the value for the array key that is the
-   * message ID, which is "${module}_${key}".
-   *
-   * For example to debug all mail sent by the user module by logging it to a
-   * file, you might set the variable as something like:
-   *
-   * @code
-   * array(
-   *   'default' => 'php_mail',
-   *   'user' => 'devel_mail_log',
-   * );
-   * @endcode
-   *
-   * Finally, a different system can be specified for a specific message ID (see
-   * the $key param), such as one of the keys used by the contact module:
-   *
-   * @code
-   * array(
-   *   'default' => 'php_mail',
-   *   'user' => 'devel_mail_log',
-   *   'contact_page_autoreply' => 'null_mail',
-   * );
-   * @endcode
-   *
-   * Other possible uses for system include a mail-sending plugin that actually
-   * sends (or duplicates) each message to SMS, Twitter, instant message, etc,
-   * or a plugin that queues up a large number of messages for more efficient
-   * bulk sending or for sending via a remote gateway so as to reduce the load
-   * on the local server.
-   *
-   * @param array $options
-   *   An array with the following key/value pairs:
-   *   - module: (string) The module name which was used by
-   *     \Drupal\Core\Mail\MailManagerInterface->mail() to invoke hook_mail().
-   *   - key: (string) A key to identify the email sent. The final message ID
-   *     is a string represented as {$module}_{$key}.
-   *
-   * @return \Drupal\Core\Mail\MailInterface
-   *   A mail plugin instance.
-   *
-   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   * {@inheritdoc}
    */
   public function getInstance(array $options) {
     $module = $options['module'];
diff --git a/core/lib/Drupal/Core/Mail/MailManagerInterface.php b/core/lib/Drupal/Core/Mail/MailManagerInterface.php
index 5cb446a..9cc43ff 100644
--- a/core/lib/Drupal/Core/Mail/MailManagerInterface.php
+++ b/core/lib/Drupal/Core/Mail/MailManagerInterface.php
@@ -125,4 +125,60 @@
    */
   public function mail($module, $key, $to, $langcode, $params = array(), $reply = NULL, $send = TRUE);
 
+  /**
+   * Overrides PluginManagerBase::getInstance().
+   *
+   * Returns an instance of the mail plugin to use for a given message ID.
+   *
+   * The selection of a particular implementation is controlled via the config
+   * 'system.mail.interface', which is a keyed array.  The default
+   * implementation is the mail plugin whose ID is the value of 'default' key. A
+   * more specific match first to key and then to module will be used in
+   * preference to the default. To specify a different plugin for all mail sent
+   * by one module, set the plugin ID as the value for the key corresponding to
+   * the module name. To specify a plugin for a particular message sent by one
+   * module, set the plugin ID as the value for the array key that is the
+   * message ID, which is "${module}_${key}".
+   *
+   * For example to debug all mail sent by the user module by logging it to a
+   * file, you might set the variable as something like:
+   *
+   * @code
+   * array(
+   *   'default' => 'php_mail',
+   *   'user' => 'devel_mail_log',
+   * );
+   * @endcode
+   *
+   * Finally, a different system can be specified for a specific message ID (see
+   * the $key param), such as one of the keys used by the contact module:
+   *
+   * @code
+   * array(
+   *   'default' => 'php_mail',
+   *   'user' => 'devel_mail_log',
+   *   'contact_page_autoreply' => 'null_mail',
+   * );
+   * @endcode
+   *
+   * Other possible uses for system include a mail-sending plugin that actually
+   * sends (or duplicates) each message to SMS, Twitter, instant message, etc,
+   * or a plugin that queues up a large number of messages for more efficient
+   * bulk sending or for sending via a remote gateway so as to reduce the load
+   * on the local server.
+   *
+   * @param array $options
+   *   An array with the following key/value pairs:
+   *   - module: (string) The module name which was used by
+   *     \Drupal\Core\Mail\MailManagerInterface->mail() to invoke hook_mail().
+   *   - key: (string) A key to identify the email sent. The final message ID
+   *     is a string represented as {$module}_{$key}.
+   *
+   * @return \Drupal\Core\Mail\MailInterface
+   *   A mail plugin instance.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException
+   */
+  public function getInstance(array $options);
+
 }
diff --git a/core/modules/rest/src/Plugin/Type/ResourcePluginManager.php b/core/modules/rest/src/Plugin/Type/ResourcePluginManager.php
index 97594c4..ecdca8d 100644
--- a/core/modules/rest/src/Plugin/Type/ResourcePluginManager.php
+++ b/core/modules/rest/src/Plugin/Type/ResourcePluginManager.php
@@ -19,7 +19,7 @@
  * @see \Drupal\rest\Plugin\ResourceInterface
  * @see plugin_api
  */
-class ResourcePluginManager extends DefaultPluginManager {
+class ResourcePluginManager extends DefaultPluginManager implements ResourcePluginManagerInterface {
 
   /**
    * Constructs a new \Drupal\rest\Plugin\Type\ResourcePluginManager object.
@@ -39,12 +39,4 @@ public function __construct(\Traversable $namespaces, CacheBackendInterface $cac
     $this->alterInfo('rest_resource');
   }
 
-  /**
-   * Overrides Drupal\Component\Plugin\PluginManagerBase::getInstance().
-   */
-  public function getInstance(array $options){
-    if (isset($options['id'])) {
-      return $this->createInstance($options['id']);
-    }
-  }
 }
diff --git a/core/modules/rest/src/Plugin/Type/ResourcePluginManagerInterface.php b/core/modules/rest/src/Plugin/Type/ResourcePluginManagerInterface.php
new file mode 100644
index 0000000..e90e9d6
--- /dev/null
+++ b/core/modules/rest/src/Plugin/Type/ResourcePluginManagerInterface.php
@@ -0,0 +1,21 @@
+<?php
+
+/**
+ * @file
+ * Definition of Drupal\rest\Plugin\Type\ResourcePluginManagerInterface.
+ */
+
+namespace Drupal\rest\Plugin\Type;
+
+use Drupal\Component\Plugin\PluginManagerInterface;
+
+/**
+ * Defines a REST resource plugin manager.
+ *
+ * @see \Drupal\rest\Annotation\RestResource
+ * @see \Drupal\rest\Plugin\ResourceBase
+ * @see \Drupal\rest\Plugin\ResourceInterface
+ * @see plugin_api
+ */
+interface ResourcePluginManagerInterface extends PluginManagerInterface {
+}
diff --git a/core/modules/rest/src/RequestHandler.php b/core/modules/rest/src/RequestHandler.php
index e205669..ff094eb 100644
--- a/core/modules/rest/src/RequestHandler.php
+++ b/core/modules/rest/src/RequestHandler.php
@@ -42,7 +42,7 @@ public function handle(RouteMatchInterface $route_match, Request $request) {
 
     $resource = $this->container
       ->get('plugin.manager.rest')
-      ->getInstance(array('id' => $plugin));
+      ->createInstance($plugin);
 
     // Deserialize incoming data if available.
     $serializer = $this->container->get('serializer');
diff --git a/core/modules/rest/src/RestPermissions.php b/core/modules/rest/src/RestPermissions.php
index 652ae1d..daba66c 100644
--- a/core/modules/rest/src/RestPermissions.php
+++ b/core/modules/rest/src/RestPermissions.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
-use Drupal\rest\Plugin\Type\ResourcePluginManager;
+use Drupal\rest\Plugin\Type\ResourcePluginManagerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
@@ -20,7 +20,7 @@ class RestPermissions implements ContainerInjectionInterface {
   /**
    * The rest resource plugin manager.
    *
-   * @var \Drupal\rest\Plugin\Type\ResourcePluginManager
+   * @var \Drupal\rest\Plugin\Type\ResourcePluginManagerInterface
    */
   protected $restPluginManager;
 
@@ -34,12 +34,12 @@ class RestPermissions implements ContainerInjectionInterface {
   /**
    * Constructs a new RestPermissions instance.
    *
-   * @param \Drupal\rest\Plugin\Type\ResourcePluginManager $rest_plugin_manager
+   * @param \Drupal\rest\Plugin\Type\ResourcePluginManagerInterface $rest_plugin_manager
    *   The rest resource plugin manager.
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
    *   The config factory.
    */
-  public function __construct(ResourcePluginManager $rest_plugin_manager, ConfigFactoryInterface $config_factory) {
+  public function __construct(ResourcePluginManagerInterface $rest_plugin_manager, ConfigFactoryInterface $config_factory) {
     $this->restPluginManager = $rest_plugin_manager;
     $this->configFactory = $config_factory;
   }
@@ -61,7 +61,7 @@ public function permissions() {
     $resources = $this->configFactory->get('rest.settings')->get('resources');
     if ($resources && $enabled = array_intersect_key($this->restPluginManager->getDefinitions(), $resources)) {
       foreach ($enabled as $key => $resource) {
-        $plugin = $this->restPluginManager->getInstance(['id' => $key]);
+        $plugin = $this->restPluginManager->createInstance($key);
         $permissions = array_merge($permissions, $plugin->permissions());
       }
     }
diff --git a/core/modules/rest/src/Routing/ResourceRoutes.php b/core/modules/rest/src/Routing/ResourceRoutes.php
index db439dc..8175365 100644
--- a/core/modules/rest/src/Routing/ResourceRoutes.php
+++ b/core/modules/rest/src/Routing/ResourceRoutes.php
@@ -10,7 +10,7 @@
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Drupal\Core\Routing\RouteSubscriberBase;
-use Drupal\rest\Plugin\Type\ResourcePluginManager;
+use Drupal\rest\Plugin\Type\ResourcePluginManagerInterface;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
@@ -24,7 +24,7 @@ class ResourceRoutes extends RouteSubscriberBase{
   /**
    * The plugin manager for REST plugins.
    *
-   * @var \Drupal\rest\Plugin\Type\ResourcePluginManager
+   * @var \Drupal\rest\Plugin\Type\ResourcePluginManagerInterface
    */
   protected $manager;
 
@@ -45,14 +45,14 @@ class ResourceRoutes extends RouteSubscriberBase{
   /**
    * Constructs a RouteSubscriber object.
    *
-   * @param \Drupal\rest\Plugin\Type\ResourcePluginManager $manager
+   * @param \Drupal\rest\Plugin\Type\ResourcePluginManagerInterface $manager
    *   The resource plugin manager.
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config
    *   The configuration factory holding resource settings.
    * @param \Psr\Log\LoggerInterface $logger
    *   A logger instance.
    */
-  public function __construct(ResourcePluginManager $manager, ConfigFactoryInterface $config, LoggerInterface $logger) {
+  public function __construct(ResourcePluginManagerInterface $manager, ConfigFactoryInterface $config, LoggerInterface $logger) {
     $this->manager = $manager;
     $this->config = $config;
     $this->logger = $logger;
@@ -71,7 +71,7 @@ protected function alterRoutes(RouteCollection $collection) {
 
     // Iterate over all enabled resource plugins.
     foreach ($enabled_resources as $id => $enabled_methods) {
-      $plugin = $this->manager->getInstance(array('id' => $id));
+      $plugin = $this->manager->createInstance($id);
 
       foreach ($plugin->routes() as $name => $route) {
         $method = $route->getRequirement('_method');