Make Element.animate work in dart2js Chrome

tests/html/element_animate_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library element_animate_test;
+
+import 'dart:async';
+import 'dart:html';
+import 'package:unittest/html_individual_config.dart';
+import 'package:unittest/unittest.dart';
+
+main() {
+  useHtmlIndividualConfiguration();
+
+  group('animate_supported', () {
+    test('supported', () {
+      expect(Notification.supported, true);
+    });
+
+    test('simple timing', () {
+      var body = document.body;
+      var opacity = num.parse(body.getComputedStyle().opacity);
+      body.animate([{"opacity": 100}, {"opacity": 0}], 100);
+      var newOpacity = num.parse(body.getComputedStyle().opacity);
+      expect(newOpacity < opacity, isTrue);
+    });
+
+    test('timing dict', () {
+      var body = document.body;
+      // Animate different characteristics so the tests can run concurrently.
+      var fontSize = body.getComputedStyle().fontSize;
+      var player = body.animate(
+          [{"font-size": "500px"}, {"font-size": fontSize}],
+          {"duration": 100});
+      var newFontSize = body.getComputedStyle().fontSize;
+      // Don't bother to parse to numbers, as long as it's changed that
+      // indicates something is happening.
+      expect(newFontSize == fontSize, isFalse);
+      player.on['finish'].listen(expectAsync((_) => 'done'));
+    });
+
+    test('omit timing', () {
+      var body = document.body;
+      var player = body.animate([
+        {"transform": "translate(100px, -100%)"},
+        {"transform": "translate(400px, 500px)"}
+      ]);
+      player.on['finish'].listen(expectAsync((_) => 'done'));
+    });
+  });
+}