Passes all dEQP tests related to etc1.

Reland: Updated to work with the D3D11 renderer and re-tested with
chromium's gles2_conform_test.

Change-Id: Id2ce1b0eb58129152f67016ce2dc3ab19208269c
Reviewed-on: https://chromium-review.googlesource.com/299770Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>