Will allow for more flexibly setting ops when we defer clears.

Bug: angleproject:4517
Change-Id: I7d9116bc92e90eb41a1030fea242eadf1cc74562
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2165629
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>