Add the option to show the size with the browser top bar visible

[Braveatom]

... i.e so that the 320 × 480 Phone (portrait) size has offsets / masks for 320px × 356px.

I guess it could be as simple as resizing the on screen boxes via a tick box, or actually showing a fake top bar.

Someone has Sizes for iPhone listed here - https://gist.github.com/1231476