At least the most important parts, I think.

Fixes #10552

Change-Id: I1a03c5405bdbef337e0245d226e9247d3d067393
Reviewed-on: https://go-review.googlesource.com/12246Reviewed-by: Andrew Gerrand <adg@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>