Add flutter_web samples (#75)

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

@@ -0,0 +1,50 @@
+// 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 GraphicsFactory, LineStyle, TextElement, TextStyle;
+import 'package:flutter_web/widgets.dart' show BuildContext, MediaQuery;
+import 'line_style.dart' show LineStyle;
+import 'text_element.dart' show TextElement;
+import 'text_style.dart' show TextStyle;
+
+class GraphicsFactory implements common.GraphicsFactory {
+  final double textScaleFactor;
+
+  GraphicsFactory(BuildContext context,
+      {GraphicsFactoryHelper helper = const GraphicsFactoryHelper()})
+      : textScaleFactor = helper.getTextScaleFactorOf(context);
+
+  /// Returns a [TextStyle] object.
+  @override
+  common.TextStyle createTextPaint() => new TextStyle();
+
+  /// Returns a text element from [text] and [style].
+  @override
+  common.TextElement createTextElement(String text) {
+    return new TextElement(text, textScaleFactor: textScaleFactor);
+  }
+
+  @override
+  common.LineStyle createLinePaint() => new LineStyle();
+}
+
+/// Wraps the MediaQuery function to allow for testing.
+class GraphicsFactoryHelper {
+  const GraphicsFactoryHelper();
+
+  double getTextScaleFactorOf(BuildContext context) =>
+      MediaQuery.textScaleFactorOf(context);
+}