This saves us from needing to replicate the same code in two places.

BUG=angleproject:956

Change-Id: Ibc80997eec184d0d5aa9c6c076c9d4507fbf8caa
Reviewed-on: https://chromium-review.googlesource.com/262776Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>