With this CL, the perf repo should now pass all tests on Windows.

Change-Id: I91fead1e065f22b54236ff96c6ace529dc3964a8
Reviewed-on: https://go-review.googlesource.com/36627
Run-TryBot: Quentin Smith <quentin@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>