build: Make enter_chroot.sh fail if run as root.

src/scripts/enter_chroot.sh

 #!/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 enter the chroot environment
 
 # Load common constants.  This should be the first executable line.
 # The path to common.sh should be relative to your script's location.
 . "$(dirname "$0")/common.sh"
 
-# Script must be run outside the chroot
+# Script must be run outside the chroot and as a regular user.
 assert_outside_chroot
+assert_not_root_user
 
 # Define command line flags
 # See http://code.google.com/p/shflags/wiki/Documentation10x
 DEFINE_string chroot "$DEFAULT_CHROOT_DIR" \
   "The destination dir for the chroot environment." "d"
 DEFINE_string trunk "$GCLIENT_ROOT" \
   "The source trunk to bind mount within the chroot." "s"
 
 DEFINE_boolean mount $FLAGS_FALSE "Only set up mounts."
 DEFINE_boolean unmount $FLAGS_FALSE "Only tear down mounts."
@@ skipping 99 matching lines @@
   REVISION="CHROMEOS_REVISION=$REVISION"
 fi
 
 # Run command or interactive shell
 sudo chroot "$FLAGS_chroot" sudo -i -u $USER $REVISION "$@"
 
 # Remove trap and explicitly unmount
 trap - EXIT
 teardown_env