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

src/scripts/common.sh

 # 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.
 
 # Common constants for build scripts
 # This must evaluate properly for both /bin/bash and /bin/sh
 
 # All scripts should die on error unless commands are specifically excepted
 # by prefixing with '!' or surrounded by 'set +e' / 'set -e'.
 # TODO: Re-enable this once shflags is less prone to dying.
@@ skipping 153 matching lines @@
 # Fail if we're inside the chroot.  This guards against creating or entering
 # nested chroots, among other potential problems.
 function assert_outside_chroot {
   if [ $INSIDE_CHROOT -ne 0 ]
   then
     echo "This script must be run outside the chroot."
     exit 1
   fi
 }
 
+function assert_not_root_user {
+  if [ `id -u` = 0 ]; then
+    echo "This script must be run as a non-root user."
+    exit 1
+  fi
+}
+
 # Install a package if it's not already installed
 function install_if_missing {
   # Positional parameters from calling script.  :? means "fail if unset".
   PKG_NAME=${1:?}
   shift
 
   if [ -z `which $PKG_NAME` ]
   then
     echo "Can't find $PKG_NAME; attempting to install it."
     sudo apt-get --yes --force-yes install $PKG_NAME
   fi
 }