class CustomBlock

1. 8.x drupal/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/Derivative/CustomBlock.php \Drupal\custom_block\Plugin\Derivative\CustomBlock
2. 8.x drupal/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/Core/Entity/CustomBlock.php \Drupal\custom_block\Plugin\Core\Entity\CustomBlock

CustomBlockTranslationUITest.php in drupal/core/modules/block/custom_block/lib/Drupal/custom_block/Tests/CustomBlockTranslationUITest.php

Contains \Drupal\custom_block\Tests\CustomBlockTranslationUITest.

custom_block.module in drupal/core/modules/block/custom_block/custom_block.module

Allows the creaation of custom blocks through the user interface.

custom_block.pages.inc in drupal/core/modules/block/custom_block/custom_block.pages.inc

Provides page callbacks for custom blocks.

custom_block_test.module in drupal/core/modules/block/custom_block/tests/modules/custom_block_test/custom_block_test.module

A dummy module for testing custom block related hooks.

class CustomBlock extends EntityNG implements CustomBlockInterface {

  /**
   * The block ID.
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $id;

  /**
   * The block revision ID.
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $revision_id;

  /**
   * Indicates whether this is the default block revision.
   *
   * The default revision of a block is the one loaded when no specific revision
   * has been specified. Only default revisions are saved to the block_custom
   * table.
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $isDefaultRevision = TRUE;

  /**
   * The block UUID.
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $uuid;

  /**
   * The custom block type (bundle).
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $type;

  /**
   * The block language code.
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $langcode;

  /**
   * The block description.
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $info;

  /**
   * The block revision log message.
   *
   * @var \Drupal\Core\Entity\Field\FieldInterface
   */
  public $log;

  /**
   * The theme the block is being created in.
   *
   * When creating a new custom block from the block library, the user is
   * redirected to the configure form for that block in the given theme. The
   * theme is stored against the block when the custom block add form is shown.
   *
   * @var string
   */
  protected $theme;

  /**
   * {@inheritdoc}
   */
  public function createDuplicate() {
    $duplicate = parent::createDuplicate();
    $duplicate->revision_id->value = NULL;
    $duplicate->id->value = NULL;
    return $duplicate;
  }

  /**
   * {@inheritdoc}
   */
  public function getRevisionId() {
    return $this->revision_id->value;
  }

  /**
   * {@inheritdoc}
   */
  public function setTheme($theme) {
    $this->theme = $theme;
  }

  /**
   * {@inheritdoc}
   */
  public function getTheme() {
    return $this->theme;
  }

  /**
   * Initialize the object. Invoked upon construction and wake up.
   */
  protected function init() {
    parent::init();

    // We unset all defined properties except theme, so magic getters apply.
    // $this->theme is a special use-case that is only used in the lifecycle of
    // adding a new block using the block library.
    unset($this->id);
    unset($this->info);
    unset($this->revision_id);
    unset($this->log);
    unset($this->uuid);
    unset($this->type);
    unset($this->new);
  }

  /**
   * {@inheritdoc}
   */
  public function uri() {
    return array(
      'path' => 'block/' . $this
        ->id(),
      'options' => array(
        'entity_type' => $this->entityType,
        'entity' => $this,
      ),
    );
  }

  /**
   * {@inheritdoc}
   */
  public function getInstances() {
    return entity_load_multiple_by_properties('block', array(
      'plugin' => 'custom_block:' . $this->uuid->value,
    ));
  }

  /**
   * {@inheritdoc}
   */
  public function delete() {
    foreach ($this
      ->getInstances() as $instance) {
      $instance
        ->delete();
    }
    parent::delete();
  }

}