Update comments for net/data/verify_certificate_chain_unittest/

net/data/verify_certificate_chain_unittest/basic-constraints-pathlen-0-self-issued/generate-chains.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 intermediates. The first intermediate has a basic
-constraints path length of 0. The second one is self-issued so does not count
-against the path length."""
+"""Certificate chain where the intermediate sets pathlen=0, and is followed by
+a self-issued intermediate."""
 
 import sys
 sys.path += ['..']
 
 import common
 
-# Self-signed root certificate (used as trust anchor).
+# Self-signed root certificate.
 root = common.create_self_signed_root_certificate('Root')
 
 # Intermediate with pathlen 0
 intermediate1 = common.create_intermediate_certificate('Intermediate', root)
 intermediate1.get_extensions().set_property('basicConstraints',
                                             'critical,CA:true,pathlen:0')
 
 # Another intermediate (with the same pathlen restriction).
 # Note that this is self-issued but NOT self-signed.
 intermediate2 = common.create_intermediate_certificate('Intermediate',
                                                        intermediate1)
 intermediate2.get_extensions().set_property('basicConstraints',
                                             'critical,CA:true,pathlen:0')
 
 # Target certificate.
 target = common.create_end_entity_certificate('Target', intermediate2)
 
 chain = [target, intermediate2, intermediate1, root]
 common.write_chain(__doc__, chain, 'chain.pem')