Add secure sockets to dart:io

runtime/bin/tls_socket.dart

+// Copyright (c) 2012, 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.
+
+abstract class TlsSocket implements Socket, Hashable {
+  /**
+   * Constructs a new secure socket and connect it to the given
+   * host on the given port. The returned socket is not yet connected
+   * but ready for registration of callbacks.
+   */
+  factory TlsSocket(String host, int port) => new _TlsSocket(host, port);
+
+  static void setCertificateDatabase(String pkcertDirectory)
+      native "TlsSocket_SetCertificateDatabase";
+}