Cache valid draw modes for draw calls. This optimizes some of our dynamic switching. It uses packed enum maps. Bug: angleproject:2747 Change-Id: Ibd2f9306d066f2fd9eb64c99a25668b7ba5c009c Reviewed-on: https://chromium-review.googlesource.com/1171505 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Frank Henigman <fjhenigman@chromium.org>