Add stub for TlsSocket to dart2js library.

lib/compiler/implementation/lib/io.dart

Index: lib/compiler/implementation/lib/io.dart
diff --git a/lib/compiler/implementation/lib/io.dart b/lib/compiler/implementation/lib/io.dart
index bac4fc23fd45cb62691e3e7683805a9b49ccc76c..41e552189f04f23a9e78e1397cb3a25789e39a56 100644
--- a/lib/compiler/implementation/lib/io.dart
+++ b/lib/compiler/implementation/lib/io.dart
@@ -54,6 +54,9 @@
 #source('../../../../runtime/bin/stream_util.dart');
 #source('../../../../runtime/bin/string_stream.dart');
 #source('../../../../runtime/bin/timer_impl.dart');
+#source('../../../../runtime/bin/tls_socket.dart');
+// Uses native keyword.
+// #source('../../../../runtime/bin/tls_socket_impl.dart');
 #source('../../../../runtime/bin/websocket.dart');
 #source('../../../../runtime/bin/websocket_impl.dart');
 
@@ -163,3 +166,9 @@ final InputStream stdin = null;
 final OutputStream stdout = null;
 
 final OutputStream stderr = null;
+
+class _TlsSocket {
+  factory TlsSocket(String host, int port) {
+    throw new UnsupportedOperationException('new TlsSocket($host, $port)');
+  }
+}