HttpCache.php

<?php

namespace Drupal\Core;

use Symfony\Component\HttpKernel\HttpCache\HttpCache as SymfonyHttpCache;

class HttpCache extends SymfonyHttpCache {
  protected function getOptions() {
    return array(
      'debug' => TRUE
    );
  }

  public function terminate(Request $request, Response $response) {
    parent::terminate($request, $response);
  }
}