missed feedback from CL

build_image

 #!/bin/bash
 
 # Copyright (c) 2009 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.
 
 # Script to build a bootable keyfob-based chromeos system image from within
 # a chromiumos setup. This assumes that all needed packages have been built into
 # the given target's root with binary packages turned on. This script will
 # build the Chrome OS image using only pre-built binary packages.
@@ skipping 132 matching lines @@
 
 # Determine build version.
 . "${SCRIPTS_DIR}/chromeos_version.sh"
 
 # Configure extra USE or packages for this type of build.
 EXTRA_PACKAGES=""
 EXTRA_USE=""
 if [ "${FLAGS_factory_install}" -eq "${FLAGS_TRUE}" ] ; then
   # Factory install needs to have the kernel initrmafs enabled,
   # and the factory installer added.
-  EXTRA_PACKAGES="chromeos-base/chromeos-factoryinstall"
-  EXTRA_USE="initramfs"
+  EXTRA_PACKAGES="${EXTRA_PACKAGES} chromeos-base/chromeos-factoryinstall"
+  EXTRA_USE="${EXTRA_USE} initramfs"
 fi
 
 # Freshen kernel with correct USE flags. This is a noop if we have
 # the right kernel prebuilt. Factory install uses USE="initramfs".
 # We don't allow building from source with the image as a target,
 # and it's not possible to store prebuilts for the same package
 # with different use flags.
 USE="${EXTRA_USE}" emerge-${FLAGS_board} \
     -uNDvg --binpkg-respect-use=y kernel
 
@@ skipping 574 matching lines @@
   echo "Developer image created as ${DEVELOPER_IMAGE_NAME}"
 fi
 
 print_time_elapsed
 
 echo "To copy to USB keyfob, OUTSIDE the chroot, do something like:"
 echo "  ./image_to_usb.sh --from=${OUTSIDE_OUTPUT_DIR} --to=/dev/sdX"
 echo "To convert to VMWare image, INSIDE the chroot, do something like:"
 echo "  ./image_to_vm.sh --from=${OUTSIDE_OUTPUT_DIR} --board=${BOARD}"
 echo "from the scripts directory where you entered the chroot."