This will pave the way for several features, like auto-generation.

BUG=angleproject:747

Change-Id: Ic390ac412f4e6b61346629093f185a4c07ea0284
Reviewed-on: https://chromium-review.googlesource.com/474118
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>