This variable can be used to override the root location of the .git
for ANGLE relative to gclient, so our DEPS can work with both
ANGLE standalone and the new bot configurations that are being
added by thakis@.

Bug: chromium:820421
Change-Id: I5cd57bc88fcd4dc69e82aa1e59d343f1eaf6f5ee
Reviewed-on: https://chromium-review.googlesource.com/1012506
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>