We were getting a warning:

stdcall calling convention ignored on variadic function

BUG=chromium:708591

Change-Id: I9165b285dfaf6bc238f946fda2d733292789390d
Reviewed-on: https://chromium-review.googlesource.com/468373Reviewed-by: Geoff Lang <geofflang@chromium.org>
(cherry picked from commit 60e17eab)
Reviewed-on: https://chromium-review.googlesource.com/469147Reviewed-by: Jamie Madill <jmadill@chromium.org>