gistfile1.yml

services:
  block.controllers:
    class: Drupal\block\BlockEntityControllers
    arguments: ['@service_container', '@module_handler']
    tags:
      - { name: event_subscriber }

gistfile2.php

<?php
/**
 * @file
 * Contains \Drupal\block\BlockEntityControllers
 */

namespace Drupal\block;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Entity\Event\EntityControllerEvent;
use Drupal\Core\Config\Entity\ConfigStorageController;

class BlockEntityControllers implements EventSubscriberInterface {

  /**
   * @var \Symfony\Component\DependencyInjection\ContainerInterface
   */
  protected $container;

  /**
   * @var \Drupal\Core\Extension\ModuleHandlerInterface
   */
  protected $moduleHandler;

  /**
   * @param ContainerInterface $container
   * @param ModuleHandlerInterface $module_handler
   */
  function __construct(ContainerInterface $container, ModuleHandlerInterface $module_handler) {
    $this->container = $container;
    $this->moduleHandler = $module_handler;
  }

  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() {
    $controllers = array(
      'storage' => 'getStorageController',
      'access' => 'getAccessController',
      'view_builder' => 'getViewBuilderController',
      'list' => 'getListController',
      'form' => 'getFormController',
    );
    $events = array();
    foreach ($controllers as $controller => $method) {
      $events["block--$controller"][] = array($method);
    }
    return $events;
  }

  /**
   * @param EntityControllerEvent $event
   */
  public function getStorageController(EntityControllerEvent $event) {
    $controller = ConfigStorageController::createInstance($this->container, $event->getEntityType());
    $event->setController($controller);
  }

  /**
   * @param EntityControllerEvent $event
   */
  public function getAccessController(EntityControllerEvent $event) {
    $controller = BlockAccessController::createInstance($this->container, $event->getEntityType());
    $controller->setModuleHandler($this->moduleHandler);
    $event->setController($controller);
  }

  public function getViewBuilderController(EntityControllerEvent $event) {
    $controller = new BlockViewBuilder();
    $event->setController($controller);
  }

  /**
   * @param EntityControllerEvent $event
   */
  public function getListController(EntityControllerEvent $event) {
    $controller = BlockListController::createInstance($this->container, $event->getEntityType());
    $event->setController($controller);
  }

  /**
   * @param EntityControllerEvent $event
   */
  public function getFormController(EntityControllerEvent $event) {
    $operation = $event->getControllerOperation();
    switch ($operation) {
      case 'default':
        $controller = \Drupal\block\BlockFormController::create($this->container);
        break;
      case 'delete':
        $controller = \Drupal\block\Form\BlockDeleteForm::create($this->container);
        break;
    }
    if ($controller) {
      $controller->setTranslationManager($this->translationManager)
        ->setModuleHandler($this->moduleHandler)
        ->setOperation($operation);
      $event->setController($controller);
    }
  }

}