Overriding or adding variables to the twig app variable

config.yml

parameters:
    templating.globals.class: Ibms\Helper\GlobalVariables

GlobalVariables.php

<?php

namespace Ibms\Helper;

use Symfony\Bundle\FrameworkBundle\Templating\GlobalVariables as BaseGlobalVariables;
use Symfony\Component\DependencyInjection\ContainerInterface;
use DateTime;

class GlobalVariables extends BaseGlobalVariables
{
    /**
     * Stores a DateTime instance.
     *
     * @var DateTime
     */
    private $dateTime;

    /**
     * Stores an array of date and time formats to be used
     * in the appliaction.
     *
     * @var array
     */
    private $formats;

    public function __construct(ContainerInterface $container)
    {
        parent::__construct($container);

        $this->dateTime = new DateTime;
    }

    public function getDate()
    {
        return $this->dateTime;
    }

    public function getRootDir()
    {
        return $this->container->get('kernel')->getRootDir();
    }

    public function getFormats()
    {
        if (!$this->formats) {
            $this->formats = array(
                'date'      => $this->container->getParameter('format.date'),
                'datetime'  => $this->container->getParameter('format.datetime'),
                'shortdate' => $this->container->getParameter('format.shortdate'),
                'time'      => $this->container->getParameter('format.time'),
            );
        }

        return $this->formats;
    }
}

This doesn't seem to work in 2.7. It uses https://github.com/symfony/TwigBridge/blob/master/AppVariable.php now. However, I can't find where this is set. Do you know where this is set @merk?