I'll update to python3 separately.

Bug: b/177465438
Change-Id: Id204789f2d0854a796e5408597700d90dc8cd191
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2626863Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@google.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>