build: Update build_image.sh for non-~/chromeos setups.

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.
@@ skipping 85 matching lines @@
   teardown_env
   exit 0
 fi
 
 # Make sure we unmount before exiting
 trap teardown_env EXIT
 setup_env
 
 if [ $FLAGS_revision -eq $FLAGS_TRUE ]
 then
-  # Get the subversion revision to pass into the chroot.  
+  # Get the subversion revision to pass into the chroot.
   #
   # This must be determined outside the chroot because (1) there is no
   # svn/git inside the chroot, and (2) if there were it would likely be
   # the wrong version, which would mess up the .svn/.git directories.
   #
   # Note that this fixes $CHROMEOS_REVISION at the time the chroot is
   # entered.  That's ok for the main use case of automated builds,
   # which pass each command line into a separate call to enter_chroot
   # so always have up-to-date info.  For developer builds, there isn't
   # really a single revision anyway, since the developer may have
   # hand-sync'd some subdirs and edited files in others.
   REVISION="$(svn info 2>&- | grep "Revision: " | awk '{print $2}')"
   if [ -z "$REVISION" ]
   then
      # Use git:8 chars of sha1
      REVISION=$(git rev-parse HEAD)
      REVISION="${REVISION:8}"
   fi
   REVISION="CHROMEOS_REVISION=$REVISION"
 fi
 
-# Run command or interactive shell
-sudo chroot "$FLAGS_chroot" sudo -i -u $USER $REVISION "$@"
+# Run command or interactive shell.  Also include the non-chrooted path to
+# the source trunk for scripts that may need to print it (e.g.
+# build_image.sh).
+sudo chroot "$FLAGS_chroot" sudo -i -u $USER $REVISION \
+  EXTERNAL_TRUNK_PATH="${FLAGS_trunk}" "$@"
 
 # Remove trap and explicitly unmount
 trap - EXIT
 teardown_env
-