See comments on https://chromium-review.googlesource.com/c/563208/. The idea is to not have duplicated Minijail cmdlines across the different invocations of the TPM firmware update scripts.

"""
that is one method.  in CL:*399810, move the business logic out of tpm-firmware-updater and into some place like /usr/share/cros/tpm-firmware-updater.sh, and have tpm-firmware-updater be a wrapper that just runs minijail/sh accordingly.  then this code turns into `chroot $USB_MNT /usr/sbin/tpm-firmware-updater`, and run_updater in CL:*400309 also gets simplified into a straight tpm-firmware-updater call.
"""