Symfony version(s) affected: master branch

Description
When trying to create any form type, a strange container require failure occurs:

How to reproduce

I have a small app that reproduces it here: https://github.com/weaverryan/bug-symfony-container-reproducer

Just start the built-in web server and go to / to see the error.

To create the reproducer app, I:

1. Created a symfony/skeleton project from dev-master
2. Installed symfony/form (dev-master)
3. Try to create a form in a controller: https://github.com/weaverryan/bug-symfony-container-reproducer/blob/master/src/Controller/ContainerTestController.php#L12

If you have any questions, please let me know! I don't think I'm doing anything funny to cause it, but you never can be sure ;).

Cheers!