shiny/driver/gldriver: implement close

The WindowResponder was being used after free because the autorelease
pool lifecycle didn't match the window cycle. Release it manually on
window being closed. While here, wire up the close logic.

Removing TODO about managing NSWindow, as the Cocoa docs say that by
default it is released when closed.

Not wiring closing into the paint loop until my other inflight paint
cycle CLs are addressed.

Fixes golang/go#12268

Change-Id: I5eb692c2dd5b302a608d0535ef191dc01e538c7f
Reviewed-on: https://go-review.googlesource.com/13871
Reviewed-by: Nigel Tao <nigeltao@golang.org>
5 files changed