This will allow us to set that certain attachments need to be
initialized in a single place.

BUG=angleproject:1635

Change-Id: I98c10206ef27670847969c726a8620c4d26400d6
Reviewed-on: https://chromium-review.googlesource.com/469150
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>