Add built-in root certificates to dart:io SecureSocket.

tests/standalone/io/secure_socket_test.dart

Index: tests/standalone/io/secure_socket_test.dart
diff --git a/tests/standalone/io/secure_socket_test.dart b/tests/standalone/io/secure_socket_test.dart
index 36386f0d9b7dfe8c282439c89413ae18747d7e73..79bfc9b6343460374ff2bf68ac8c3804cb8ba00c 100644
--- a/tests/standalone/io/secure_socket_test.dart
+++ b/tests/standalone/io/secure_socket_test.dart
@@ -26,9 +26,7 @@ void WriteAndClose(Socket socket, String message) {
 }
 
 void main() {
-  var testPkcertDatabase =
-      new Path.fromNative(new Options().script).directoryPath.append('pkcert/');
-  SecureSocket.setCertificateDatabase(testPkcertDatabase.toNativePath());
+  SecureSocket.initialize();
   // TODO(3593): Use a Dart HTTPS server for this test.
   // When we use a Dart HTTPS server, allow --short_socket_write. The flag
   // causes fragmentation of the client hello message, which doesn't seem to