Use ShaderBitSet for active use bits on uniforms BUG=angleproject:2169 Change-Id: I192c2e3c453540c8a6d7b0d066218ea3c9fbaab2 Reviewed-on: https://chromium-review.googlesource.com/989411 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>