This is a reland of f38f54f2

Original change's description:
> Add optional enforce_fetch kwarg to fetch and refresh git cache
>
> Allows builders to do a force refresh of the git cache to ensure a new
> fetch happens. android-binary-size needs this to get an accurate diff
> of the passed in src revision and the applied patch:
> https://bugs.chromium.org/p/chromium/issues/detail?id=1129235#c19
>
> Bug: 1129235
> Change-Id: I993521cdde2a491fc9d42d75ff28dedcd2cea64e
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2438802
> Commit-Queue: Stephanie Kim <kimstephanie@google.com>
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>

Bug: 1129235
Change-Id: I034a91a8b57821d08b10042f7fc94d32350540ba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2443235Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Stephanie Kim <kimstephanie@google.com>