Add flutter_web samples (#75)

web/charts/flutter/lib/src/util/color.dart

@@ -0,0 +1,28 @@
+// 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 Color;
+import 'package:flutter_web_ui/ui.dart' as ui;
+
+class ColorUtil {
+  static ui.Color toDartColor(common.Color color) {
+    return ui.Color.fromARGB(color.a, color.r, color.g, color.b);
+  }
+
+  static common.Color fromDartColor(ui.Color color) {
+    return common.Color(
+        r: color.red, g: color.green, b: color.blue, a: color.alpha);
+  }
+}