Update pipeline description with depth offset state.  Enable test.

BUG=angleproject:2353

Change-Id: Ib087bbff8e145b0e6e862eb6616a4943a989a7b2
Reviewed-on: https://chromium-review.googlesource.com/1173447
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>