Pack firmware into an image and do update in factory install (separated git).

factory_install.sh

 #!/bin/sh -e
 
 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 . "$(dirname "$0")/chromeos-common.sh"
 . "/opt/google/memento_updater/memento_updater_logging.sh"
 
 if [ $(id -u) -ne 0 ]; then
   echo "You must run this as root."
   exit 1
 fi
 log "Pause to ensure ethernet connectivity"
 sleep 10
 
 # TODO(adlr): pick an install device in a matter that works on x86 and ARM.
 # This works on x86 only, afaik.
-DST=/dev/sda
+DST_DRIVE=/dev/sda
 DST_FACTORY_PART=3
 DST_RELEASE_PART=5
 DST_OEM_PART=8
 DST_EFI_PART=12
 DST_STATE_PART=1
+DST_FIRMWARE=/tmp/firmware.sh
 
 log "Factory Install: Setting partition table"
 
-/usr/sbin/chromeos-install --dst "${DST}" --skip_rootfs --run_as_root --yes \
-  2>&1 | cat >> "$MEMENTO_AU_LOG"
+/usr/sbin/chromeos-install --dst "${DST_DRIVE}" --skip_rootfs --run_as_root \
+  --yes 2>&1 | cat >> "$MEMENTO_AU_LOG"
 
 # Load the new partition table. The autoupdater has trouble with loop devices.
 sync
 echo 3 > /proc/sys/vm/drop_caches
-/sbin/sfdisk -R "$DST"
+/sbin/sfdisk -R "$DST_DRIVE"
 
 FACTORY_CHANNEL_ARG='--force_track=factory-channel'
 RELEASE_CHANNEL_ARG='--force_track=release-channel'
 OEM_CHANNEL_ARG='--force_track=oempartitionimg-channel'
 EFI_CHANNEL_ARG='--force_track=efipartitionimg-channel'
 STATE_CHANNEL_ARG='--force_track=stateimg-channel'
+FIRMWARE_CHANNEL_ARG='--force_track=firmware-channel'
 
 # Install the partitions
-for i in EFI OEM STATE RELEASE FACTORY; do
-  PART=$(eval "echo \$DST_${i}_PART")
+for i in EFI OEM STATE RELEASE FACTORY FIRMWARE; do
+  if [ "$i" = "FIRMWARE" ]; then
+    DST="${DST_FIRMWARE}"
+  else
+    PART=$(eval "echo \$DST_${i}_PART")
+    DST="${DST_DRIVE}${PART}"
+  fi
+
+  log "Factory Install: Installing $i image to $DST"
+
   CHANNEL_ARG=$(eval "echo \$${i}_CHANNEL_ARG")
+  SKIP_POSTINST_ARG="--skip_postinst"
   KPART="none"
-
-  log "Factory Install: Installing $i partition to $PART"
-
-  SKIP_POSTINST_ARG="--skip_postinst"
   if [ "$i" = "FACTORY" -o "$i" = "RELEASE" ]; then
     # Set up kernel partition
     SKIP_POSTINST_ARG=""
     KPART=""
   fi
 
   RESULT="$(/opt/google/memento_updater/memento_updater.sh --dst_partition \
-    "${DST}${PART}" --kernel_partition "${KPART}" \
+    "${DST}" --kernel_partition "${KPART}" \
     --allow_removable_boot $CHANNEL_ARG $SKIP_POSTINST_ARG)"
 
-  if [ "$RESULT" != "UPDATED" ]; then
+  # Firmware update is optional; still OK if it does not be updated.
+  if [ "$RESULT" != "UPDATED" -a "$i" != "FIRMWARE" ]; then
     log "Factory Install: AU failed"
     exit 1
   fi
 done
 
 log "All done installing."
 
 shutdown -r now
 sleep 1d  # sleep indefinitely to avoid respawning rather than shutting down