Migrate presubmit to python3

Changed the python scripts to work with python3. To resolve
a small difference in test output, I changed the expectation,
and now only run the tests for Python 3.

Bug: 1212099
Change-Id: Id9aec5e2958a3e119bb6187789c19b39300a0472
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2934658
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Dan H <harringtond@chromium.org>
Cr-Commit-Position: refs/heads/master@{#890323}
NOKEYCHECK=True
GitOrigin-RevId: f4a602ec74259319a6308d1d41ec21b9192bc4dd
8 files changed