See symfony/symfony#22620

Some classes have been moved, so we must review the imports of the code samples:

• The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\AddCacheClearerPass
  class has been deprecated and will be removed in 4.0. Use the
  Symfony\Component\HttpKernel\DependencyInjection\AddCacheClearerPass class instead.

• The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\AddCacheWarmerPass
  class has been deprecated and will be removed in 4.0. Use the
  Symfony\Component\HttpKernel\DependencyInjection\AddCacheWarmerPass class instead.