Eliminates lots of ad hoc code for recognizing the same thing in
different ways.

Passes toolstash-check.

Change-Id: Ic0bb005308e96331b4ef30f455b860e476725b61
Reviewed-on: https://go-review.googlesource.com/73190
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>