Refactor some certificate verification tests in preparation to adding

net/data/verify_certificate_chain_unittest/generate-unknown-root.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, but the root is not in trust store.
 Verification is expected to fail because the final intermediate (Intermediate)
 does not chain to a known root."""
 
 import common
 
-# Self-signed root certificate, which is NOT added to the trust store.
+# Self-signed root certificate, which is NOT saved as the trust anchor.
 root = common.create_self_signed_root_certificate('Root')
 
 # Intermediate certificate.
 intermediate = common.create_intermediate_certificate('Intermediate', root)
 
 # Target certificate.
 target = common.create_end_entity_certificate('Target', intermediate)
 
+# Self-signed root certificate, not part of chain, which is saved as trust
+# anchor.
+bogus_root = common.create_self_signed_root_certificate('BogusRoot')
+
 chain = [target, intermediate]
-trusted = []  # Note that this lacks |root|
+trusted = common.TrustAnchor(bogus_root, constrained=False)
 time = common.DEFAULT_TIME
 verify_result = False
 
 common.write_test_file(__doc__, chain, trusted, time, verify_result)