This contains https://crrev.com/c/2465408, which has a workaround to
make ${vpython_platform} work on Python 3.

Bug: 1123433
Change-Id: I62eb96b8caaae5b954a06f6bdcbd1169200f3523
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2465360
Auto-Submit: Owen Rodley <orodley@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>