Use active textures mask with robust init. This should speed up clearUnclearedActiveTextures considerably. It was showing up as a hotspot when running the aquarium demo with the passthrough command decoder. Also rename the complete textures mask in gl::State to an active textures mask, since it includes incomplete textures. BUG=angleproject:2188 Change-Id: Idf020fc49c1e74f17a8005c3b88516829767b84c Reviewed-on: https://chromium-review.googlesource.com/722421 Reviewed-by: Frank Henigman <fjhenigman@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>