Add flutter_web samples (#75)

web/gallery/lib/demo/material/switch_demo.dart

@@ -0,0 +1,42 @@
+// 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/demo.dart';
+
+class SwitchDemo extends StatefulWidget {
+  static const routeName = '/material/switch';
+
+  @override
+  SwitchDemoState createState() => SwitchDemoState();
+}
+
+class SwitchDemoState extends State<SwitchDemo> {
+  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();
+
+  @override
+  Widget build(BuildContext context) {
+    return wrapScaffold('Switch Demo', context, _scaffoldKey, _buildContents(),
+        SwitchDemo.routeName);
+  }
+
+  bool _value = true;
+
+  Widget _buildContents() {
+    return Material(
+      child: Column(
+        children: [
+          Switch(
+              value: _value,
+              onChanged: (bool newValue) {
+                setState(() {
+                  _value = newValue;
+                });
+              }),
+        ],
+      ),
+    );
+  }
+}