The EME Extension, Policy Check API allows web developers to query the status
of a hypothetical key associated with an HDCP policy, without the need to
create a MediaKeySession or fetch a real license. It does not
require the MediaKeys to be attached to any
HTMLMediaElement either. If HDCP is available at the specified
version, the promise should return a MediaKeyStatus of "usable".
Note: In Chrome 69, it is available for trials so
that websites can use it without any experimental flag.