Proposal: drop `allowpaymentrequest` attribute

[marcoscaceres]

Current state of things:

• Only Chrome implements and ships allowpaymentrequest. Safari never implemented it, and Firefox never shipped it outside of Nightly. Payment Request has been disabled for 2+ years in Firefox, and seems unlikely to ship as Mozilla lacks a backing Payment Handler implementation. Work on implementing Payment Handler was put on hold.
• Permissions Policy spec defines "payment", allowing the allow= to explicitly override allowpaymentrequest.
• In Chrome, the allowpaymentrequest attribute is not implemented per spec, leading to some WPT failures.

As such, I'm wondering if it might be prudent to remove allowpaymentrequest from HTML (and from Permission Policy and from Payment Request).

If we agree, we would need to update:

• html
• Permission Policy spec
• The Payment Request API spec.

CC @danyao @rsolomakhin @adrianhopebailie

[danyao]

+1

[ianbjacobs]

+1

[danyao]

Filed Chrome tracking bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1127988