Add scripts to generate simple test data for certificate verification.

net/data/verify_certificate_chain_unittest/generate-violates-basic-constraints-pathlen-0.py

+#!/usr/bin/python
+# Copyright (c) 2015 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.
+
+"""Certificate chain with 2 intermediaries. The first intermediary has a basic
+constraints path length of 0, so it is a violation for it to have a subordinate
+intermediary."""
+
+import common
+
+# Self-signed root certificate (part of trust store).
+root = common.create_self_signed_root_certificate('Root')
+
+# Intermediary with pathlen 0
+intermediary1 = common.create_intermediary_certificate('Intermediary1', root)
+intermediary1.get_extensions().set_property('basicConstraints',
+                                            'critical,CA:true,pathlen:0')
+
+# Another intermediary (with the same pathlen restriction)
+intermediary2 = common.create_intermediary_certificate('Intermediary2',
+                                                       intermediary1)
+intermediary2.get_extensions().set_property('basicConstraints',
+                                            'critical,CA:true,pathlen:0')
+
+# Target certificate.
+target = common.create_end_entity_certificate('Target', intermediary2)
+
+chain = [target, intermediary2, intermediary1]
+trusted = [root]
+time = common.DEFAULT_TIME
+verify_result = False
+
+common.write_test_file(__doc__, chain, trusted, time, verify_result)