Cross-browser testing of ARIA IDL reflection and accessibility values

[rahimabdi]

The ARIA WG is investigating enhancements to ARIA IDL via conversion of some attributes to be truly enumerated attributes (see https://github.com/w3c/aria/issues/2281). Although currently blocked by testability, it would be valuable to verify ARIA content attribute value reflection in JavaScript for ensuring consistency across browsers and particularly, what is actually exposed by the a11y tree for content/IDL attributes.

One particular attribute (tracked in this bug) that is treated differently across browsers at present is aria-checked; aria-checked=“foo” on a role=“switch” element is exposed as “on” for macOS VoiceOver/Chrome but “off” for macOS VoiceOver/Safari. Ideally, the aria-checked content attribute should be conveyed as false via AT and its IDL attribute (ariaChecked) for invalid values.

[zcorpan]

This seems testable as-is with wpt infra.