I found a couple of bugs trying to enable polygon offset render states.

This is just pre-work to get to a better state.

Bug:angleproject:2353

Change-Id: If6af949a09af1340e870afb627ae427d01c6e77c
Reviewed-on: https://chromium-review.googlesource.com/975631
Commit-Queue: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>