/usr/lib/curtin/helpers/install-grub is in curtin-common 0.1.0~bzr126-0ubuntu1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 | #!/bin/bash
[ "${0%/*}" = "$0" ] && . ./common || . "${0%/*}/common"
install_grub "$@"
|