[mediacapture-main] What constraint name should be exposed in case of a getUserMedia query with multiple failing constraints (#562)

youennf has just created a new issue for https://github.com/w3c/mediacapture-main:

== What constraint name should be exposed in case of a getUserMedia query with multiple failing constraints ==
Crafting a getUserMedia request that always fails allows guessing the capabilities of a system, in particular if the request has one constraint that is known to always fail and a second constraint that may or may not fail.

Some potential countermeasures:
- Not return the failing constraint name if getUserMedia is not already granted
- Return the constraint name that can never be met

Please view or discuss this issue at https://github.com/w3c/mediacapture-main/issues/562 using your GitHub account