Add flutter_web samples (#75)

web/charts/example/lib/a11y/a11y_gallery.dart

@@ -0,0 +1,29 @@
+// 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';
+import '../gallery_scaffold.dart';
+import 'domain_a11y_explore_bar_chart.dart';
+
+List<GalleryScaffold> buildGallery() {
+  return [
+    new GalleryScaffold(
+      listTileIcon: new Icon(Icons.accessibility),
+      title: 'Screen reader enabled bar chart',
+      subtitle: 'Requires TalkBack or Voiceover turned on to work. '
+          'Bar chart with domain selection explore mode behavior.',
+      childBuilder: () => new DomainA11yExploreBarChart.withRandomData(),
+    ),
+  ];
+}