Config provides a way to concurrently access Width and Height.
Register provides a way for packages to run code on app state change
without plumbing changes all the way to the process main function.
This is motivated by gl/glutil.Image which needs to rebuild its
textures on start/stop and can be deeply nested.
(See golang.org/cl/9707 for the followup.)
Tested manually on android and darwin/amd64. Doing this kind makes it
clear any CL modifying this code needs a lot of manual testing right
now, so some kind of trybot support is something I'm going to
prioritise.
Fixesgolang/go#10686Fixesgolang/go#10461Fixesgolang/go#10442Fixesgolang/go#10226
Updates golang/go#10327
Change-Id: I2882ebf3995b6ed857cda823e94fbb17c54b43a8
Reviewed-on: https://go-review.googlesource.com/9708
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
