This will more easily allow us to use a cached completeness comparison
value. The cached value only gets updated on certain setters.

Bug: angleproject:2763
Change-Id: Ib80db8517560617087ae8360f7af69d6c2392b76
Reviewed-on: https://chromium-review.googlesource.com/1171507Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>