Does the TODOs added by https://golang.org/cl/7623.

Passes rsc.io/toolstash/buildall.

Change-Id: I23913a8f03834640e9795d48318febb3f88c10f9
Reviewed-on: https://go-review.googlesource.com/9160Reviewed-by: Russ Cox <rsc@golang.org>