Remove base level from texture storage.

BUG=angle:596

Change-Id: I66173f77b6c5aed3b8836cd2c9f1da02ae769429
Reviewed-on: https://chromium-review.googlesource.com/192056
Tested-by: Nicolas Capens <nicolascapens@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
12 files changed