use log2(scale) to compute mip level

now w/ expanded suppressions

This reverts commit b50ced703030dfbda4fc3ef5e6ec9a52fc0405f8.

BUG=skia:
TBR=
NOTRY=True
NOTREECHECKS=True

Review URL: https://codereview.chromium.org/856723003
4 files changed