Update comments for net/data/verify_certificate_chain_unittest/

net/data/verify_certificate_chain_unittest/target-has-keycertsign-but-not-ca/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 1 intermediate, a trusted root, and a target
-certificate that is not a CA, and yet has the keyCertSign bit set. Verification
-is expected to fail, since keyCertSign should only be asserted when CA is
-true."""
+"""Certificate chain where the leaf certificate asserts the keyCertSign key
+usage, however does not have CA=true in the basic constraints extension to
+indicate it is a CA."""
 
 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 certificate.
 intermediate = common.create_intermediate_certificate('Intermediate', root)
 
 # Target certificate (end entity but has keyCertSign bit set).
 target = common.create_end_entity_certificate('Target', intermediate)
 target.get_extensions().set_property('keyUsage',
     'critical,digitalSignature,keyEncipherment,keyCertSign')
 
 chain = [target, intermediate, root]
 common.write_chain(__doc__, chain, 'chain.pem')