We were missing both the correct SRV parameter, as well as the full
computation of the mip level in the HLSL.

Re-land makes the mip computation only happen with implicit sampling.
Before it would confuse the LOD0 computation.

BUG=angleproject:1208
TEST=dEQP-GLES3.functional.texture.*

Change-Id: I4b579033afe5cd1aca1f2d017e48a74c7fc324cc
Reviewed-on: https://chromium-review.googlesource.com/314330
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>