The DisplayUnit interface inherits availWidth, availHeight, width, height, colorDepth, and pixelDepth from the Screen interface [CSSOM].

This means that these should be physical value / current devicePixelRatio. This needs testing! Tests setting deviceScaleFactor to something != 1 and comparing with the values in window.screen. It should also set a page zoom (aka browser zoom) and compare and a mixture of those two!