Switch to a whitelist for manual mip-map generation

Due to performance regression on various GPUs, we're only going to use the
new draw-call based mip-mapper when necessary. Of the bots where we have
test coverage, that means Intel and Mac-NVIDIA. We also had failures on
our AMD 7770 bots - I'm upgrading the drivers on those two machines, and
I'm leaving them out of the whitelist for now.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2042313002

Review-Url: https://codereview.chromium.org/2042313002
3 files changed