Autofill forms detected/loaded is in UMA already (See sample chart - https://docs.google.com/document/d/15sflYSw3BnlKIriEV7cJ9abJYOdZQHsLGrWWt_HkS3E/edit#heading=h.6ti50l30yu4f).

But we dont have that sliced by credit cards form types. 

>> Why we need this metric

Understand payment drop off %. Merchants complain that people drop off forms (because they dont have credit card in hand, takes time to fill it on mobile, ...). The idea is to be pro active to inform users that they can use autofill and encourage them to finish transaction. 

We will get corresponding data from GA as a comparison and see if it makes case for more pro-active UIs. 

If we have time, let us try to re-produce that chart here.