Add flutter_web samples (#75)

web/gallery/lib/main.dart

@@ -0,0 +1,11 @@
+// Copyright 2018 The Chromium Authors. 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:flutter_web/material.dart';
+
+import 'gallery/app.dart';
+
+void main() {
+  runApp(GalleryApp());
+}