I missed this one in codereview.appspot.com/70010050
Same thing, but different test.

Fixes windows-amd64-race and likely other Windows
machines failing like:
http://build.golang.org/log/0382bf0048bf5835a51a8a902df5c6fc73cd7ff5

LGTM=adg
R=rsc, adg
CC=golang-codereviews
https://golang.org/cl/71770043