Merge in the flutter gallery (#176)

gallery/l10n_cli/bin/main.dart

@@ -0,0 +1,9 @@
+// Copyright 2019 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:l10n_cli/l10n_cli.dart' as l10n_cli;
+
+main(List<String> arguments) async {
+  await l10n_cli.englishArbsToXmls();
+}