Re: [mediacapture-main] Broken foreground detection (#752)

What a system focus requirement provides `enumerateDevices()` is that there would (usually) be only one focused browsing context hierarchy on a system.
With only a visibility test, there would often be more than one "visible" top-level browsing context on a user's desktop, [allowing fingerprinting across origins](https://github.com/w3c/mediacapture-main/issues/561).  Visibility is typically not strict, and so a browsing context is typically considered visible even when fully occluded by another system window, and some desktop systems do not promote minimization of inactive windows.

The disadvantage of the focus requirement is that sometimes the presence of a device is useful for [displaying items that would be visible before any user interaction](https://github.com/w3c/mediacapture-main/issues/905).

Visibility seems the preferred requirement for `enumerateDevices()` and "devicechange" if fingerprinting exposure can be comparable to focus.
For example, if delaying the exposure of device changes by returning an old list of devices for a long enough unpredictable period of time would reduce the correlation between origins sufficiently, then the list of devices would at least be available and accurate when the devices haven't changed recently.

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Received on Monday, 31 October 2022 05:59:04 UTC