Avoid lint of couple of files we did not author.

colortrans.py, pstat.py and stats.py were not written by us and we are
not maintaining them. They don't comply to our coding conventions. So,
it does not make sense to lint them.

BUG=chromium:570456
    chromium:567921
TEST=None (trivial)

Change-Id: I20469396a55f6d5da0d73f5c7d33204fe6728c33
Reviewed-on: https://chrome-internal-review.googlesource.com/243258
Commit-Ready: Luis Lozano <llozano@chromium.org>
Tested-by: Luis Lozano <llozano@chromium.org>
Reviewed-by: Luis Lozano <llozano@chromium.org>
3 files changed