AU: when generating payload, only delta generation needs to be in chroot

cros_generate_update_payload

 #!/bin/bash
 
 # 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.
 
 # Script to generate a Chromium OS update for use by the update engine.
 # If a source .bin is specified, the update is assumed to be a delta update.
 
 # Load common constants.  This should be the first executable line.
@@ skipping 74 matching lines @@
   sudo losetup -o "$offset" "$STATE_LOOP_DEV" "$IMAGE"
   STATE_MNT=$(mktemp -d /tmp/state.XXXXXX)
   sudo mount "$STATE_LOOP_DEV" "$STATE_MNT"
   dd if="$STATE_MNT"/vmlinuz_hd.vblock of="$KERN_FILE" conv=notrunc
   sudo umount "$STATE_MNT"
   STATE_MNT=""
   sudo losetup -d "$STATE_LOOP_DEV"
   STATE_LOOP_DEV=""
 }
 
-# We should be in the chroot.
-assert_inside_chroot
-
 DEFINE_string image "" "The image that should be sent to clients."
 DEFINE_string src_image "" "Optional: a source image. If specified, this makes\
  a delta update."
 DEFINE_boolean old_style "$FLAGS_TRUE" "Generate an old-style .gz full update."
 DEFINE_string output "" "Output file"
 DEFINE_boolean patch_kernel "$FLAGS_FALSE" "Whether or not to patch the kernel \
 with the patch from the stateful partition (default: false)"
 
 # Parse command line
 FLAGS "$@" || exit 1
 eval set -- "${FLAGS_ARGV}"
 
 set -e
 
+if [ -n "$FLAGS_src_image" ]; then
+  # We need to be in the chroot for generating delta images
+  assert_inside_chroot
+fi
+
 locate_gpt
 
 DELTA=$FLAGS_TRUE
 [ -n "$FLAGS_output" ] || die \
     "Error: you must specify an output filename with --output FILENAME"
 
 if [ -z "$FLAGS_src_image" ]; then
   DELTA=$FLAGS_FALSE
   if [ "$FLAGS_old_style" = "$FLAGS_TRUE" ]; then
     echo "Generating an old-style full update"
@@ skipping 53 matching lines @@
   
   GENERATOR="$(dirname "$0")/mk_memento_images.sh"
 
   CROS_GENERATE_UPDATE_PAYLOAD_CALLED=1 "$GENERATOR" "$DST_KERNEL" "$DST_ROOT"
   mv "$(dirname "$DST_KERNEL")/update.gz" "$FLAGS_output"
   
   trap - INT TERM EXIT
   cleanup noexit
   echo "Done generating full update."
 fi