Independent control center windows come up at the wrong
size at startup and then resize as the content fills
in.

This looks quite bad.

What should happen is that it should wait for the contents
before mapping the window (though this is annoying in
another way if the capplet is too slow.)

It shouldn't be too hard to implement it - control-center-signal
just has to check socket->plug_window until it becomes non-NULL.
This could be done in a 10-times-per-second timeout, or
possible a little harder while (!socket->plug_winndow) g_main_iteration.
Hardest thing here is probalby taking care of the failure case
where the child doesn't start at all.