Add flutter_web samples (#75)

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

@@ -0,0 +1,79 @@
+// 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 ChipDemo extends StatefulWidget {
+  static const routeName = '/material/chip';
+  @override
+  State<StatefulWidget> createState() => _ChipDemoState();
+}
+
+class _ChipDemoState extends State<ChipDemo> {
+  bool _filterChipSelected = false;
+  bool _hasAvatar = true;
+
+  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();
+
+  @override
+  Widget build(BuildContext context) {
+    return wrapScaffold('Chip Demo', context, _scaffoldKey, _buildContents(),
+        ChipDemo.routeName);
+  }
+
+  Widget _buildContents() {
+    return Material(
+        child: Column(
+      children: [
+        addPadding(Chip(
+          label: Text('Chip'),
+        )),
+        addPadding(InputChip(
+          label: Text('InputChip'),
+        )),
+        addPadding(ChoiceChip(
+          label: Text('Selected ChoiceChip'),
+          selected: true,
+        )),
+        addPadding(ChoiceChip(
+          label: Text('Deselected ChoiceChip'),
+          selected: false,
+        )),
+        addPadding(FilterChip(
+          label: Text('FilterChip'),
+          selected: _filterChipSelected,
+          onSelected: (bool newValue) {
+            setState(() {
+              _filterChipSelected = newValue;
+            });
+          },
+        )),
+        addPadding(ActionChip(
+          label: Text('ActionChip'),
+          onPressed: () {},
+        )),
+        addPadding(ActionChip(
+          label: Text('Chip with avatar'),
+          avatar: _hasAvatar
+              ? CircleAvatar(
+                  backgroundColor: Colors.amber,
+                  child: Text('Z'),
+                )
+              : null,
+          onPressed: () {
+            setState(() {
+              _hasAvatar = !_hasAvatar;
+            });
+          },
+        )),
+      ],
+    ));
+  }
+}
+
+Padding addPadding(Widget widget) => Padding(
+      padding: EdgeInsets.all(10.0),
+      child: widget,
+    );