Try this syntax instead, it will log the new tasks name to the AppEngine logs as proof that the task was created:
require_once 'google/appengine/api/taskqueue/PushTask.php';
use \google\appengine\api\taskqueue\PushTask;
$task_name = (new PushTask('/worker/anchorextractor/1', array(
'content_id' => 'aa',
'content_type' => 'aa'
)))->add("tagextractor");
syslog(LOG_INFO, "new task=".$task_name);
Tasks do get processed very quickly, so it is sometimes difficult to "see" them in the queue, you can however go to the queue in the admin console and pause it, the tasks will then build up until you either run it manually or resume the queue.