Test filling small mips of ETC textures.
Test filling small mips of ETC textures.

BUG=angleproject:1510

Change-Id: I9ed7c877767909ba93e2ea5ef09c4735b0d0bcc7
Reviewed-on: https://chromium-review.googlesource.com/382652
Commit-Queue: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

ppy/angle,ecoal95/angle,ecoal95/angle,ecoal95/angle,ecoal95/angle,ecoal95/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,MSOpenTech/angle,ppy/angle,MSOpenTech/angle,ppy/angle