This should be a refactoring change only. The new code is exercised in
follow-up CLs.

BUG=angleproject:754

Change-Id: I99285e1e7772cae467013102f25c911ebc9f54a9
Reviewed-on: https://chromium-review.googlesource.com/309153Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>