This is a WebGL spec change:
https://github.com/KhronosGroup/WebGL/commit/bfbe124a7bb92eed34ea7cc18694167ed66b1030

Fixes conformance2/textures/misc/tex-mipmap-levels.html

Bug: chromium:898351
Change-Id: Ib20409e10bec598611be273577115a380a63b523
Reviewed-on: https://chromium-review.googlesource.com/c/1352385
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>