Watching for permission changes

[marcoscaceres]

Get user media, and I suspect other specs, want to be notified of permission changes (independent of the API eventing model).

I wonder if we should have some kind of subscription model in our spec for that?

The Page Visibility spec has something similar, like the "external now visible visible algorithm"... I don't know if that's quite ideal, but something like that could work.

@jyasskin, wdyt?

[marcoscaceres]

Here is an example from GetUserMedia:

For each device that {{MediaDevices/getUserMedia()}} exposes, whenever a transition occurs of the
[=permission state=] of the permission associated with the device's kind
and the device's deviceId, deviceId, run the following
steps:

[jyasskin]

It looks like https://w3c.github.io/mediacapture-main/#mediadevices does distinct things when the permission state becomes "granted" vs when it becomes not-"granted". I had imagined that the permission revocation algorithm would handle the "becomes not-granted" case, and the spec could handle the ->granted case itself around the call to https://www.w3.org/TR/permissions/#requesting-more-permission.

I wouldn't object to doing this some other way.