drupal_depth_first_search() moved to Drupal\Component\Graph\Graph

In light of the core subsystems move to PSR-4 autoloading, the drupal_depth_first_search() function has been moved to a Graph class.

Drupal 7

require_once DRUPAL_ROOT . '/includes/graph.inc';
drupal_depth_first_search($graph);

Drupal 8

use Drupal\Component\Graph\Graph;

$graph_object = new Graph($graph);
$graph = $graph_object->searchAndSort($graph);