1. Not to assert inside chroot, if so desired.

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 101 matching lines @@
     patch_kernel "$bin_file" "$kern_out"
   fi
   extract_partition_to_temp_file "$bin_file" 3 "$root_out"
 }
 
 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 "$FLAGS_TRUE" "Generate an old-style .gz full update."
 DEFINE_string output "" "Output file"
+DEFINE_boolean outside_chroot "$FLAGS_FALSE" "Running outside of chroot."
 DEFINE_boolean patch_kernel "$FLAGS_FALSE" "Whether or not to patch the kernel \
 with the patch from the stateful partition (default: false)"
 DEFINE_string private_key "" "Path to private key in .pem format."
 DEFINE_boolean extract "$FLAGS_FALSE" "If set, extract old/new kernel/rootfs \
 to [old|new]_[kern|root].dat. Useful for debugging (default: false)"
 DEFINE_boolean full_kernel "$FLAGS_FALSE" "Generate a full kernel update even \
 if generating a delta update (default: false)"
 
 # Parse command line
 FLAGS "$@" || exit 1
 eval set -- "${FLAGS_ARGV}"
 
 set -e
 
-if [ -n "$FLAGS_src_image" ]; then
-  # We need to be in the chroot for generating delta images
+if [ -n "$FLAGS_src_image" ] && \
+   [ "$FLAGS_outside_chroot" -eq "$FLAGS_FALSE" ]; then
+  # We need to be in the chroot for generating delta images.
+  # by specifying --outside_chroot you can choose not to assert
+  # this will allow us to run this script outside chroot.
+  # Running this script outside chroot requires copying delta_generator binary
+  # and also copying few shared libraries with it.
   assert_inside_chroot
 fi
 
 locate_gpt
 
 if [ "$FLAGS_extract" -eq "$FLAGS_TRUE" ]; then
   if [ -n "$FLAGS_src_image" ]; then
     extract_kern_root "$FLAGS_src_image" old_kern.dat old_root.dat
   fi
   if [ -n "$FLAGS_image" ]; then
@@ skipping 47 matching lines @@
   fi
   DST_ROOT=$(extract_partition_to_temp_file "$FLAGS_image" 3)
 
   if [ "$DELTA" -eq "$FLAGS_TRUE" ]; then
     SRC_MNT=$(mktemp -d /tmp/src_root.XXXXXX)
     sudo mount -o loop,ro "$SRC_ROOT" "$SRC_MNT"
 
     DST_MNT=$(mktemp -d /tmp/src_root.XXXXXX)
     sudo mount -o loop,ro "$DST_ROOT" "$DST_MNT"
 
-    sudo "$GENERATOR" \
+    sudo LD_LIBRARY_PATH=${LD_LIBRARY_PATH}  PATH=${PATH} "$GENERATOR" \
         -new_dir "$DST_MNT" -new_image "$DST_ROOT" -new_kernel "$DST_KERNEL" \
         -old_dir "$SRC_MNT" -old_image "$SRC_ROOT" -old_kernel "$SRC_KERNEL" \
         -out_file "$FLAGS_output" -private_key "$FLAGS_private_key"
   else
     "$GENERATOR" \
         -new_image "$DST_ROOT" -new_kernel "$DST_KERNEL" \
         -out_file "$FLAGS_output" -private_key "$FLAGS_private_key"
   fi
 
   trap - INT TERM EXIT
@@ skipping 16 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