Add flutter_web samples (#75)

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

@@ -0,0 +1,98 @@
+// 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 _PageSelector extends StatelessWidget {
+  const _PageSelector({this.icons});
+
+  final List<Icon> icons;
+
+  void _handleArrowButtonPress(BuildContext context, int delta) {
+    final TabController controller = DefaultTabController.of(context);
+    if (!controller.indexIsChanging)
+      controller
+          .animateTo((controller.index + delta).clamp(0, icons.length - 1));
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final TabController controller = DefaultTabController.of(context);
+    final Color color = Theme.of(context).accentColor;
+    return SafeArea(
+      top: false,
+      bottom: false,
+      child: Column(
+        children: <Widget>[
+          Container(
+              margin: const EdgeInsets.only(top: 16.0),
+              child: Row(children: <Widget>[
+                IconButton(
+                    icon: const Icon(Icons.chevron_left),
+                    color: color,
+                    onPressed: () {
+                      _handleArrowButtonPress(context, -1);
+                    },
+                    tooltip: 'Page back'),
+                TabPageSelector(controller: controller),
+                IconButton(
+                    icon: const Icon(Icons.chevron_right),
+                    color: color,
+                    onPressed: () {
+                      _handleArrowButtonPress(context, 1);
+                    },
+                    tooltip: 'Page forward')
+              ], mainAxisAlignment: MainAxisAlignment.spaceBetween)),
+          Expanded(
+            child: IconTheme(
+              data: IconThemeData(
+                size: 128.0,
+                color: color,
+              ),
+              child: TabBarView(
+                  children: icons.map<Widget>((Icon icon) {
+                return Container(
+                  padding: const EdgeInsets.all(12.0),
+                  child: Card(
+                    child: Center(
+                      child: icon,
+                    ),
+                  ),
+                );
+              }).toList()),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+class PageSelectorDemo extends StatelessWidget {
+  static const String routeName = '/material/page-selector';
+  static final List<Icon> icons = <Icon>[
+    const Icon(Icons.event, semanticLabel: 'Event'),
+    const Icon(Icons.home, semanticLabel: 'Home'),
+    const Icon(Icons.android, semanticLabel: 'Android'),
+    const Icon(Icons.alarm, semanticLabel: 'Alarm'),
+    const Icon(Icons.face, semanticLabel: 'Face'),
+    const Icon(Icons.language, semanticLabel: 'Language'),
+  ];
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Page selector'),
+        actions: <Widget>[MaterialDemoDocumentationButton(routeName)],
+      ),
+      body: DefaultTabController(
+        length: icons.length,
+        child: _PageSelector(icons: icons),
+      ),
+    );
+  }
+}