Add --with_dev_pkgs option to build_image.sh to pull in developer debug packages.

src/package_repo/package-list-debug.txt

Index: src/package_repo/package-list-debug.txt
diff --git a/src/package_repo/package-list-debug.txt b/src/package_repo/package-list-debug.txt
new file mode 100644
index 0000000000000000000000000000000000000000..69a8d3c7221826d1c3d70694ab4a990390f167f2
--- /dev/null
+++ b/src/package_repo/package-list-debug.txt
@@ -0,0 +1,26 @@
+# Copyright (c) 2009 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This file contains the list of packages we install to assist
+# developers. One package per line.
+
+apt
+bootchart
+bsdutils
+bzip2
+diff
+ifupdown
+iproute
+iputils-ping
+less
+ncurses-base
+net-tools
+openssh-server
+tar
+vim-tiny
+x11-utils
+xterm
+
+# needed by apt-get to verify signatures
+gnupg