Answer

Answer
Lokið

The new version 2 adds a new tool in the extension's popup which allows you to open a page in a chrome-less window, removing this way the minimum width/height restrictions.

Those restrictions can also be bypassed by zooming in the page.

Under review

The settings for phone/tablet resolutions will be implemented in a completely different way than it is right now, which will fix this problem.

I'm also thinking of doing something similar to Firefox's Ctrl+Shift+M (probably Cmd+Shift+M on Mac OS).

There is problem with size below around 300px (bar in top must have no icon to resize for this width).
Need to open in new window for this small resolution without bar,icon etc (like in RWD tester they create new window)
Only for this small resolution because its no possible to work. 
Thanks for great chrome extension. In work is help full. :)
Answer
Lokið

The new version 2 adds a new tool in the extension's popup which allows you to open a page in a chrome-less window, removing this way the minimum width/height restrictions.

Those restrictions can also be bypassed by zooming in the page.