Passes toolstash -cmp.

Update #14473.

Change-Id: I2ac5c595d7af7a8da1a7e3945e6a753299446250
Reviewed-on: https://go-review.googlesource.com/20497
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>