Go 1.8 doesn't have t.Helper.

Fix the row of red on the dashboard.

Change-Id: I85d4bb9fe38e989dc3b6a4e99705599745b83cef
Reviewed-on: https://go-review.googlesource.com/80140
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tom Bergan <tombergan@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>