make cryptohome check a magic file to discern between chrome-login and slim-login

src/platform/cryptohome/bin/mount

 #!/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.
 
 set -e  # exit on failure
 set -E  # share the error handler
 set -u  # require all variables to be defined
 USERID=""
 PASSWORD=""
 
 function error_handler() {
   if ! typeset -F cryptohome::log; then
     echo "An error occurred before/in cryptohome." 1>&2
     # Assume common is ok.
-    /bin/mount -t tmpfs tmpfs /home/$DEFAULT_USER
-    /bin/chown $DEFAULT_USER /home/$DEFAULT_USER
+    /bin/mount -t tmpfs tmpfs $DEFAULT_MOUNT_POINT
+    /bin/chown $DEFAULT_USER $DEFAULT_MOUNT_POINT
     exit 1
   fi
 
   local image="$IMAGE_DIR/${USERID}/image"
   cryptohome::log "entering the mount error_handler ($image)"
   # We don't want to error out again if close fails
   cryptohome::close || $true
   # Same goes for detach
   cryptohome::detach || $true
   if [[ -n "$image" ]]; then
     cryptohome::log "removing the failed image: $image"
     $rm -f $image
   fi
   cryptohome::log "attempting to create a new image..."
   # Let's try a new image. If that fails, use the exit trap.
   trap second_chance EXIT
   cryptohome::mount_or_create "$USERID" "$PASSWORD"
   trap - EXIT
   cryptohome::log "new image created and mounted successfully"
   cryptohome::log "mount completed"
   $exit 0
 }
 # TODO: move traps into a single call
 trap error_handler ERR;
 
 function second_chance() {
   cryptohome::log "new image creation failed (again)"
   cryptohome::log "mounting tmpfs"
-  $mount -t tmpfs tmpfs /home/$DEFAULT_USER
-  $chown $DEFAULT_USER /home/$DEFAULT_USER
+  $mount -t tmpfs tmpfs $DEFAULT_MOUNT_POINT
+  $chown $DEFAULT_USER $DEFAULT_MOUNT_POINT
   cryptohome::log "mount completed"
   $exit 0
 }
 
 function mount_main() {
   if ! typeset -p CHROMEOS_USER &>/dev/null  ; then
     cryptohome::log "CHROMEOS_USER not exported."
     cryptohome::log "Assuming we aren't coming via pam_google..."
     return 0
   fi
@@ skipping 18 matching lines @@
 }
 
 # Invoke main.
 if [[ "${BASH_SOURCE[0]}" == "$0" ]]; then
   source "$(dirname "$0")/../lib/chromeos-cryptohome/common"
   utils::declare_commands exit
   # Everything is done by default at present.
   mount_main
 fi