This chat window works with the new chat tabs, with minimal wasted space.
Quite compact because it doesn't draw all the border lines and empty space around the many parts of the window. But all the standard features still exist, all at normal size. Even though you can't see them, you can drag by the title bar, resize by the edges, and of course the input bar still works even if it doesn't have a line drawn around it.
BTW, I recommend a height of 220 for this window. At that size, the standard arial font will show only full-lines of text, even if you switch between font sizes 1, 2, 3, and 4.