This is a reland of dc8e23d3

Original change's description:
> git-cl: Keep git push traces
> 
> Keep the last N git push traces.
> Name them after the time when they were collected, and add a
> README file to each one to provide some context to developers.
> 
> Bug: 955206
> Change-Id: Ib5fcf2f78fb65f6ddd80a93619c14e1ef70c5564
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1595108
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
> Reviewed-by: Dirk Pranke <dpranke@chromium.org>

Bug: 955206
Change-Id: Ie63a3ebfe3024d48ad7e0c8492a2939e635371aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1600246Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>