payerEmail attribute

Click on each button in sequence from top to bottom without refreshing the page. Each button will bring up the Payment Request UI window.

When requested, please use "wpt@w3.org" as the email.

1. payerEmail attribute is null when options undefined.
2. payerEmail attribute is null when requestPayerEmail is undefined.
3. payerEmail attribute is null when requestPayerEmail is false.
4. payerEmail attribute is 'wpt@w3.org' when requestPayerEmail is true.
5. payerEmail attribute is 'wpt@w3.org' when requestPayerEmail is truthy.