Every time the user selects Android Pay (for example) in PaymentRequest, Chrome should increment the count and update the last use time of using that particular payment app.

This information should be stored in a new autofill table.

This information should be synchronized, which requires a new sync protobuf and sync controller.

Frecency algorithm for PaymentRequest payments should include both credit cards and payment apps on equal footing.

Also need to use website's ordering of payment methods as a signal in the sorting algorithm.