This moves as much code outside the protocol generator
as possible making it easier to maintain both the code
and the generator.
Change-Id: I7fe932a58facece5bb0bd5a9c158e5cc7d5a277b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/236838
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>