Intent to Ship: CloseWatcher

[Keith Cirkel]

Summary: CloseWatcher

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1859702

Specification: https://html.spec.whatwg.org/#close-requests-and-close-watchers

Standards Body: HTML WG

Platform coverage: All

Preference: dom.closewatcher.enabled

Devtools bug: N/A

Other browsers:

  - Blink: Shipping since M126 (https://chromestatus.com/feature/4722261258928128).

  - WebKit: Neutral, however they are partially implemented (https://github.com/WebKit/WebKit/pull/21939).

web-platform-tests: https://wpt.fyi/results/close-watcher

Gecko-only tests were introduced: N/A

I intend to enable this in nightly very shortly, to then subsequently enable by default. Unless any issues arise, I intend to ship this in the 140 milestone, but I am also happy to defer this to 141 if we need to.

This feature is tightly integrated with Dialog & Popover elements, but there is no hard dependency on either, the `closedby` "light dismiss" attribute on Dialogs also is intended to ship in 140 but they are not inter-dependant so either one can miss the 140 release without impacting the other.

If anyone has any concerns please let me know!

Happy browsing.

[Nicolas Chevobbe]

Thanks Keith.

I filed https://bugzilla.mozilla.org/show_bug.cgi?id=1966702 to properly handle the new `close` and `cancel` events in DevTools Debugger (they should appear in the Event listeners breakpoints list, as well as in the Tracer panel)