Add flutter_web samples (#75)

web/charts/example/lib/pie_chart/pie_gallery.dart

@@ -0,0 +1,65 @@
+// 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 'auto_label.dart';
+import 'donut.dart';
+import 'gauge.dart';
+import 'simple.dart';
+import 'outside_label.dart';
+import 'partial_pie.dart';
+
+List<GalleryScaffold> buildGallery() {
+  return [
+    new GalleryScaffold(
+      listTileIcon: new Icon(Icons.pie_chart),
+      title: 'Simple Pie Chart',
+      subtitle: 'With a single series',
+      childBuilder: () => new SimplePieChart.withRandomData(),
+    ),
+    new GalleryScaffold(
+      listTileIcon: new Icon(Icons.pie_chart),
+      title: 'Outside Label Pie Chart',
+      subtitle: 'With a single series and labels outside the arcs',
+      childBuilder: () => new PieOutsideLabelChart.withRandomData(),
+    ),
+    new GalleryScaffold(
+      listTileIcon: new Icon(Icons.pie_chart),
+      title: 'Partial Pie Chart',
+      subtitle: 'That doesn\'t cover a full revolution',
+      childBuilder: () => new PartialPieChart.withRandomData(),
+    ),
+    new GalleryScaffold(
+      listTileIcon: new Icon(Icons.pie_chart),
+      title: 'Simple Donut Chart',
+      subtitle: 'With a single series and a hole in the middle',
+      childBuilder: () => new DonutPieChart.withRandomData(),
+    ),
+    new GalleryScaffold(
+      listTileIcon: new Icon(Icons.pie_chart),
+      title: 'Auto Label Donut Chart',
+      subtitle:
+          'With a single series, a hole in the middle, and auto-positioned labels',
+      childBuilder: () => new DonutAutoLabelChart.withRandomData(),
+    ),
+    new GalleryScaffold(
+      listTileIcon: new Icon(Icons.pie_chart),
+      title: 'Gauge Chart',
+      subtitle: 'That doesn\'t cover a full revolution',
+      childBuilder: () => new GaugeChart.withRandomData(),
+    ),
+  ];
+}