Fails on the bots, on ReadPixelsTest.DrawWithPBO/ES3_D3D11

BUG=angleproject:940

This reverts commit ada5d07e.

Change-Id: I60c71af6317f6b5ee1bf1555cb4573c5e82a11d6
Reviewed-on: https://chromium-review.googlesource.com/317430Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>