According to the spec(section 18.1), all copy commands are treated
as transfer operations for the purposes of synchronization
barriers. Some tests are flaky on Intel platform without such
barriers.

Bug: angleproject:2663
Bug: angleproject:2664
Change-Id: Ic8bc9a0eb000670342c0df0449257324f04ad1f8
Reviewed-on: https://chromium-review.googlesource.com/1124103
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>