This adds support for gracefully shutting down the Server, including
sending a GOAWAY frame to clients and shutting down when things are
idle. For now this support is only when integrated with the standard
A future change could export some of this.
Run-TryBot: Brad Fitzpatrick <email@example.com>
TryBot-Result: Gobot Gobot <firstname.lastname@example.org>
Reviewed-by: Ian Lance Taylor <email@example.com>