Add flutter_web samples (#75)

web/charts/example/lib/drawer.dart

@@ -0,0 +1,51 @@
+// Copyright 2018 the Charts project authors. Please see the AUTHORS file
+// for details.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import 'package:flutter_web/material.dart';
+
+/// A menu drawer supporting toggling theme and performance overlay.
+class GalleryDrawer extends StatelessWidget {
+  final bool showPerformanceOverlay;
+  final ValueChanged<bool> onShowPerformanceOverlayChanged;
+
+  GalleryDrawer(
+      {Key key,
+      this.showPerformanceOverlay,
+      this.onShowPerformanceOverlayChanged})
+      : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return new Drawer(
+      child: new ListView(children: <Widget>[
+        // Performance overlay toggle.
+        new ListTile(
+          leading: new Icon(Icons.assessment),
+          title: new Text('Performance Overlay'),
+          onTap: () {
+            onShowPerformanceOverlayChanged(!showPerformanceOverlay);
+          },
+          selected: showPerformanceOverlay,
+          trailing: new Checkbox(
+            value: showPerformanceOverlay,
+            onChanged: (bool value) {
+              onShowPerformanceOverlayChanged(!showPerformanceOverlay);
+            },
+          ),
+        ),
+      ]),
+    );
+  }
+}