mount method
Mounts handler
as the base handler for this server.
All requests to url or and URLs beneath it will be sent to handler
until close is called.
Throws a StateError if there's already a handler mounted.
Implementation
@override
void mount(Handler handler) {
if (_mounted) {
throw StateError("Can't mount two handlers for the same server.");
}
_mounted = true;
serveRequests(server, handler);
}