[mediacapture-main] Move enumerateDevices behind permission (#612)

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

== Move enumerateDevices behind permission ==
Currently websites can enumerate hardware capabilities with enumerateDevices().  Querying device capabilities is the kind of pseudo-identifier that allow users to be passively identified / fingerprinted.  To prevent this, websites should, to the greatest degree possible, need user permission to query device capabilities.  Websites should therefor need permission to access enumerateDevices().

Related: the Moz efforts discussed at the bottom of this comment : https://github.com/w3c/mediacapture-main/issues/607#issuecomment-514460424

Please view or discuss this issue at https://github.com/w3c/mediacapture-main/issues/612 using your GitHub account