Add flutter_web samples (#75)

web/charts/flutter/lib/src/behaviors/calculation/percent_injector.dart

@@ -0,0 +1,72 @@
+// 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 PercentInjector, PercentInjectorTotalType;
+import 'package:meta/meta.dart' show immutable;
+
+import '../chart_behavior.dart' show ChartBehavior, GestureType;
+
+/// Chart behavior that can inject series or domain percentages into each datum.
+///
+/// [totalType] configures the type of total to be calculated.
+///
+/// The measure values of each datum will be replaced by the percent of the
+/// total measure value that each represents. The "raw" measure accessor
+/// function on [MutableSeries] can still be used to get the original values.
+///
+/// Note that the results for measureLowerBound and measureUpperBound are not
+/// currently well defined when converted into percentage values. This behavior
+/// will replace them as percents to prevent bad axis results, but no effort is
+/// made to bound them to within a "0 to 100%" data range.
+///
+/// Note that if the chart has a [Legend] that is capable of hiding series data,
+/// then this behavior must be added after the [Legend] to ensure that it
+/// calculates values after series have been potentially removed from the list.
+@immutable
+class PercentInjector extends ChartBehavior<common.PercentInjector> {
+  final desiredGestures = new Set<GestureType>();
+
+  /// The type of data total to be calculated.
+  final common.PercentInjectorTotalType totalType;
+
+  PercentInjector._internal({this.totalType});
+
+  /// Constructs a [PercentInjector].
+  ///
+  /// [totalType] configures the type of data total to be calculated.
+  factory PercentInjector({common.PercentInjectorTotalType totalType}) {
+    totalType ??= common.PercentInjectorTotalType.domain;
+    return new PercentInjector._internal(totalType: totalType);
+  }
+
+  @override
+  common.PercentInjector<D> createCommonBehavior<D>() =>
+      new common.PercentInjector<D>(totalType: totalType);
+
+  @override
+  void updateCommonBehavior(common.PercentInjector commonBehavior) {}
+
+  @override
+  String get role => 'PercentInjector';
+
+  @override
+  bool operator ==(Object o) {
+    return o is PercentInjector && totalType == o.totalType;
+  }
+
+  @override
+  int get hashCode => totalType.hashCode;
+}