Control media elements test cases
When playing video inside a nested iframe, we expect that fullscreen mode will be enabled if either the allowfullscreen attribute is set or if the allow attribute contains fullscreen for the parent iframe. Fullscreen settings for ancestor iframes higher up in the hierarchy is not expected to affect the behavior. The controlslist attribute will be ignored (even if nofullscreen is set).
Nested iframe, top level iframe doesn't allow fullscreen. Video iframe does.
Expect: fullscreen mode enabled in offscreen menu.
Nested iframe, top level iframe doesn't allow fullscreen. Video iframe does. controlslist='nofullscreen' set on video.
Expect: fullscreen mode enabled in offscreen menu
Nested iframe, top level iframe allows fullscreen. Video iframe doesn't allow fullscreen.
Expect: fullscreen mode disabled in offscreen menu.