Set active window to certain width and height

I would like to have the functionality to set the width and height of any active application window. In this widget I would set the preferred window size to be f.i. 1280 x 800. Selecting the widget in the menu bar would size the active window to 1280 x 800.
This functionality is well known for browser windows, but I want it on all windows.

 

Toolbox 5.1 bring this feature!