We shouldn't need to special case the barrier logic in this function
any more. Instead use the 'onBufferRead' and 'onBufferWrite' APIs.

Bug: angleproject:4029
Change-Id: I7f67b67aa312d9ae64172b40d73086b7772d49d2
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2071143
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>