Relevant documentation: https://docs.python.org/3/library/sys.html#sys.platform

Bug: 1007872
Change-Id: Id4bb6e1da1d3244fcd245569fd74fd204ce1e9ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1824843
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Auto-Submit: Victor Costan <pwnall@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>