The only upside of fetching everything directly from GoB
is that git cache would get just 1 .pack. However, git cache
already runs "git gc" before uploading cache to GS, so
this point is moot.

R=maruel

Bug: 943696
Change-Id: Ie8e77a81aa81489dae240b7c767c5842a12c6f19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1585641Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>