git map: Add -h option
git map: Add -h option

Bug:

Change-Id: Ife7f4049062bc951e58d5c322b1fc7e39338fe79
Reviewed-on: https://chromium-review.googlesource.com/463246
Commit-Queue: anatoly techtonik <657222fa4408d5fb9c49497617f580f8c5974a3b@gmail.com>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools