This fixes a D3D11 runtime warning in perf test init. We don't
see it on the bots because we don't typically enable the D3D11
runtime.

BUG=angleproject:2188

Change-Id: I512db7d5a34204f1d94e28d80cadb18f9b17e55f
Reviewed-on: https://chromium-review.googlesource.com/724738
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>