How to implement Android's contacts list scroll index effect?

I would like to achieve Android contact's list scroll effect.

I found some similar custom implementations but not the same.

As always, Google creates awesome experiences on its default apps but doesn't add it to the native framework library.

This scrollbar is available on the contacts list since KitKat =/

UPDATE

I found in Android Developers page this list of contacts example and they're implementing this exact effect.

Years later I found this cool L4Digital/FastScroll library that easily achieves the exact same effect I was looking for.

We're working with this library in production with a large user base app w/o any problem.