This works around GL drivers that neglect to clamp the base level or
max level of immutable textures.

BUG=angleproject:596
BUG=610800
TEST=angle_end2end_tests

Change-Id: Ie4e04aaa9253f2befd73bccefa7759486b3ef487
Reviewed-on: https://chromium-review.googlesource.com/344590Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>