Useful when runnig the same test both on Python 2 and Python 3.

Change-Id: I6074e4cbd64318985cf438a2d491182b7b9ccc7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1913259Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>