$ git clone -n https://src.fedoraproject.org/rpms/chromium.git /var/lib/mock/f40-build-1945503-25181/root/chroot_tmpdir/scmroot/chromium
Cloning into '/var/lib/mock/f40-build-1945503-25181/root/chroot_tmpdir/scmroot/chromium'...
$ git fetch origin ae2d0f9ee63f688b390fc292dfd0db35b27e5129:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/chromium
 * [new ref]         ae2d0f9ee63f688b390fc292dfd0db35b27e5129 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ae2d0f9 Merge branch 'rawhide' into f40