Add flutter_web samples (#75)

web/charts/flutter/test/text_element_test.dart

@@ -0,0 +1,39 @@
+// 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' show BuildContext;
+import 'package:mockito/mockito.dart';
+import 'package:test/test.dart';
+import 'package:charts_flutter/src/graphics_factory.dart';
+import 'package:charts_flutter/src/text_element.dart';
+
+class MockContext extends Mock implements BuildContext {}
+
+class MockGraphicsFactoryHelper extends Mock implements GraphicsFactoryHelper {}
+
+void main() {
+  test('Text element gets assigned scale factor', () {
+    final helper = new MockGraphicsFactoryHelper();
+    when(helper.getTextScaleFactorOf(any)).thenReturn(3.0);
+    final graphicsFactory =
+        new GraphicsFactory(new MockContext(), helper: helper);
+
+    final textElement =
+        graphicsFactory.createTextElement('test') as TextElement;
+
+    expect(textElement.text, equals('test'));
+    expect(textElement.textScaleFactor, equals(3.0));
+  });
+}