Re-enable chroot passthru for AU server environment variable override

enter_chroot.sh

Index: enter_chroot.sh
diff --git a/enter_chroot.sh b/enter_chroot.sh
index 973d1980490a19929d441983a2b9f86d45bf5aa1..bd39e722937a669d068c80e551c28e8aa9ace635 100755
--- a/enter_chroot.sh
+++ b/enter_chroot.sh
@@ -355,6 +355,15 @@ CHROOT_PASSTHRU="BUILDBOT_BUILD=$FLAGS_build_number CHROMEOS_OFFICIAL=$CHROMEOS_
 CHROOT_PASSTHRU="${CHROOT_PASSTHRU} \
 CHROMEOS_RELEASE_APPID=${CHROMEOS_RELEASE_APPID:-"{DEV-BUILD}"}"
 
+# Set CHROMEOS_VERSION_TRACK, CHROMEOS_VERSION_AUSERVER,
+# CHROMEOS_VERSION_DEVSERVER as environment variables to override the default
+# assumptions (local AU server). These are used in cros_set_lsb_release, and
+# are used by external Chromium OS builders.
+CHROOT_PASSTHRU="${CHROOT_PASSTHRU} \
+CHROMEOS_VERSION_TRACK=${CHROMEOS_VERSION_TRACK} \
+CHROMEOS_VERSION_AUSERVER=${CHROMEOS_VERSION_AUSERVER} \
+CHROMEOS_VERSION_DEVSERVER=${CHROMEOS_VERSION_DEVSERVER}"
+
 if [ -d "$HOME/.subversion" ]; then
   TARGET="/home/${USER}/.subversion"
   mkdir -p "${FLAGS_chroot}${TARGET}"