IPC::ClientConnection now tracks the time since the last time we got
a message from the client and calls a virtual function on itself after
3 seconds: may_have_become_unresponsive().
Subclasses of ClientConnection can then react to this if they like.
We use this mechanism in WindowServer to send out a friendly Ping
message to the client. If he doesn't Pong within 1 second, we mark
the client as "unresponsive" and recompose all of his windows with
a darkened appearance and amended title until he Pongs us.
This is a little on the aggressive side and we should figure out a way
to wake up less often. Perhaps this could only be done to windows the
user is currently interacting with, for example.
Anyways, this is pretty cool! :^)
