Control media elements test cases
When playing video inside an iframe, we expect that fullscreen mode will be enabled if either the allowfullscreen attribute is set or if the allow attribute contains fullscreen. The controlslist attribute will be ignored (even if nofullscreen is set).
Iframe without allowfullscreen, allow='fullscreen' attributes
Expect: fullscreen mode disabled in offscreen menu.
Iframe with allowfullscreen attribute
Expect: fullscreen mode enabled in offscreen menu.
Iframe with allow='fullscreen' attribute
Expect: fullscreen mode enabled in offscreen menu.
Iframe with allow='fullscreen' attribute and with controlslist='nofullscreen'
Expect: fullscreen mode enabled in offscreen menu.