Add script that generates X509 certificates for testing dart:io SecureSocket

tests/standalone/io/localhost_v3_extensions

Index: tests/standalone/io/localhost_v3_extensions
diff --git a/tests/standalone/io/localhost_v3_extensions b/tests/standalone/io/localhost_v3_extensions
new file mode 100644
index 0000000000000000000000000000000000000000..99cc4d1ee8c257939fdd1f20d8e7f8e67ea3876a
--- /dev/null
+++ b/tests/standalone/io/localhost_v3_extensions
@@ -0,0 +1,18 @@
+# Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+
+# OpenSSL configuration file giving the v3 extensions for the localhost
+# server certificate
+subjectAltName = @alt_names
+basicConstraints = CA:false
+subjectKeyIdentifier=hash
+authorityKeyIdentifier=keyid,issuer
+
+[alt_names]
+DNS.1 = localhost
+DNS.2 = 127.0.0.1
+DNS.3 = ::1
+IP.1 = 127.0.0.1
+IP.2 = ::1
+