||AutoplayPolicy is used to manage autoplay logic for all kinds of media,
including MediaElement, Web Audio and Web Speech.
Autoplay could be disable by setting the pref "media.autoplay.default"
to anything but nsIAutoplay::Allowed. Once user disables autoplay, media
could only be played if one of following conditions is true.
1) Owner document is activated by user gestures
We restrict user gestures to "mouse click", "keyboard press" and "touch".
2) Muted media content or video without audio content.
3) Document's origin has the "autoplay-media" permission.
||This class is used to provide an ability for GeckoView (GV) to allow its
embedder (application) to decide whether the autoplay media should be allowed
or denied on the page. We have two types of request, one for audible media,
another one for inaudible media. Each page would at most have one request per
type at a time, and the result of request would be effective on that page
until the page gets reloaded or closed.
||Possible values for the "media.autoplay.default" preference.