Add flutter_web samples (#75)

web/charts/flutter/lib/src/pie_chart.dart

@@ -0,0 +1,54 @@
+// 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:charts_common/common.dart' as common
+    show ArcRendererConfig, PieChart, RTLSpec, Series;
+import 'behaviors/chart_behavior.dart' show ChartBehavior;
+import 'base_chart.dart' show BaseChart, LayoutConfig;
+import 'base_chart_state.dart' show BaseChartState;
+import 'selection_model_config.dart' show SelectionModelConfig;
+
+class PieChart<D> extends BaseChart<D> {
+  PieChart(
+    List<common.Series> seriesList, {
+    bool animate,
+    Duration animationDuration,
+    common.ArcRendererConfig<D> defaultRenderer,
+    List<ChartBehavior> behaviors,
+    List<SelectionModelConfig<D>> selectionModels,
+    common.RTLSpec rtlSpec,
+    LayoutConfig layoutConfig,
+    bool defaultInteractions: true,
+  }) : super(
+          seriesList,
+          animate: animate,
+          animationDuration: animationDuration,
+          defaultRenderer: defaultRenderer,
+          behaviors: behaviors,
+          selectionModels: selectionModels,
+          rtlSpec: rtlSpec,
+          layoutConfig: layoutConfig,
+          defaultInteractions: defaultInteractions,
+        );
+
+  @override
+  common.PieChart<D> createCommonChart(BaseChartState chartState) =>
+      new common.PieChart<D>(layoutConfig: layoutConfig?.commonLayoutConfig);
+
+  @override
+  void addDefaultInteractions(List<ChartBehavior> behaviors) {
+    super.addDefaultInteractions(behaviors);
+  }
+}