The types for this were a bit disorganized. Clean this up.

BUG=angleproject:1635

Change-Id: I669d347697e0c7c5b06ed7165fa0997c375e876e
Reviewed-on: https://chromium-review.googlesource.com/483315
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>