Comment 7 for bug 876017

Difficulty: Medium
Method:
1) Make unity depend on the scale plugin
2) Make unity::UnityWindow inherit from ScaleWindow
3) Make UnityWindow overload scalePaintDecoration
4) Load a small texture asset with an X button (or appropriate equavilent) and paint it at the correct location when appropriate
Test: The main thing for testing here is the code to position the texture in the right place over the window. I believe ScalePaintDecoration gives you a ScaleSlot, which you can use to determine the geometry of the scaled window, from there we just need to test that our code puts the button in the right place for that geometry