PaymentRequest show() rejects if doc is not fully active

Click on each button in sequence from top to bottom without refreshing the page. Each button will bring up the Payment Request UI window and then will close it automatically. (If a payment sheet stays open, the test has failed.)

1. PaymentRequest.show() aborts if the document is not active.
2. PaymentRequest.show() aborts if the document is active, but not fully active.
3. Done!