Fix Portage for users who picked up portage-2.2.12-r4.

BUG=chromium:428112
TEST=Run it, confirm portage is emerged

Change-Id: Idb5d2b10865f3922deb34c4e30b010b6115fb7f7
Reviewed-on: https://chromium-review.googlesource.com/226042
Reviewed-by: Daniel Erat <derat@chromium.org>
Tested-by: David James <davidjames@chromium.org>
diff --git a/chroot_version_hooks.d/100_emerge_portage b/chroot_version_hooks.d/100_emerge_portage
new file mode 100644
index 0000000..7213be5
--- /dev/null
+++ b/chroot_version_hooks.d/100_emerge_portage
@@ -0,0 +1,6 @@
+# Copyright 2014 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.
+
+# If users are stuck on a bad version of Portage, update it.
+sudo emerge -u portage