This was showing up in BlitFramebufferPerf.Run/d3d11_depth_2_samples.
It would only show up when running the perf tests with the D3D11
Debug layer enabled.

BUG=angleproject:2188

Change-Id: I71f310641d4a4c017e8c4c907c2bdc61019978a4
Reviewed-on: https://chromium-review.googlesource.com/724962Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>