Synchronous getUserMedia proposal

In its simplest form:

MediaStream getUserMedia(MediaConstraints constraints);

This returns a stream that provides no content (open option: a tainted
stream that can only be displayed locally).

Consent is indicated with a new onconsent event on the stream; failure
reuses the onended event.  A new reason parameter is added to the onended
event indicating the reason (this includes all existing onended reason
codes, if any, plus all getUserMedia error codes).

The major complaint with this is that it leads to an inaccurate/misleading
expectation about the usability of the stream.  That expectation can lead
to the assumption that consent is granted, which would be a bad assumption.