Add flutter_web samples (#75)

web/gallery/lib/demo/shrine_demo.dart

@@ -0,0 +1,43 @@
+// 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 'shrine/shrine_home.dart' show ShrineHome;
+import 'shrine/shrine_theme.dart' show ShrineTheme;
+
+// This code would ordinarily be part of the MaterialApp's home. It's being
+// used by the ShrineDemo and by each route pushed from there because this
+// isn't a standalone app with its own main() and MaterialApp.
+Widget buildShrine(BuildContext context, Widget child) {
+  return Theme(
+      data: ThemeData(
+        primarySwatch: Colors.grey,
+        iconTheme: const IconThemeData(color: Color(0xFF707070)),
+        platform: Theme.of(context).platform,
+      ),
+      child: ShrineTheme(child: child));
+}
+
+// In a standalone version of this app, MaterialPageRoute<T> could be used directly.
+class ShrinePageRoute<T> extends MaterialPageRoute<T> {
+  ShrinePageRoute({
+    WidgetBuilder builder,
+    RouteSettings settings,
+  }) : super(builder: builder, settings: settings);
+
+  @override
+  Widget buildPage(BuildContext context, Animation<double> animation,
+      Animation<double> secondaryAnimation) {
+    return buildShrine(
+        context, super.buildPage(context, animation, secondaryAnimation));
+  }
+}
+
+class ShrineDemo extends StatelessWidget {
+  static const String routeName = '/shrine'; // Used by the Gallery app.
+
+  @override
+  Widget build(BuildContext context) => buildShrine(context, ShrineHome());
+}