Save the private keys used by generated verify_certificate_chain tests.

net/data/verify_certificate_chain_unittest/generate-target-signed-using-ecdsa.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 a trusted root using RSA, and intermediate using EC,
 and a target certificate using RSA. Verification is expected to succeed."""
 
 import common
 
 # Self-signed root certificate (used as trust anchor). using RSA.
 root = common.create_self_signed_root_certificate('Root')
 
 # Intermediate using an EC key for the P-384 curve.
 intermediate = common.create_intermediate_certificate('Intermediate', root)
-intermediate.set_key(common.generate_ec_key('secp384r1'))
+intermediate.set_key(common.get_or_generate_ec_key(
+    'secp384r1', common.create_key_path(intermediate.name)))
 
 # Target certificate contains an RSA key (but is signed using ECDSA).
 target = common.create_end_entity_certificate('Target', intermediate)
 
 chain = [target, intermediate]
 trusted = common.TrustAnchor(root, constrained=False)
 time = common.DEFAULT_TIME
 key_purpose = common.DEFAULT_KEY_PURPOSE
 verify_result = True
 errors = None
 
 common.write_test_file(__doc__, chain, trusted, time, key_purpose,
                        verify_result, errors)