Add all dart:html tests from the sdk to test/codegen.

test/codegen/lib/html/messageevent_test.dart

+library SerializedScriptValueTest;
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+import 'dart:html';
+
+main() {
+  useHtmlConfiguration();
+
+  test('new MessageEvent', () {
+      final event = new MessageEvent('type', cancelable: true, data: 'data',
+          origin: 'origin', lastEventId: 'lastEventId');
+
+      expect(event.type, equals('type'));
+      expect(event.bubbles, isFalse);
+      expect(event.cancelable, isTrue);
+      expect(event.data, equals('data'));
+      expect(event.origin, equals('origin'));
+      // IE allows setting this but just ignores it.
+      // expect(event.lastEventId, equals('lastEventId'));
+      expect(event.source, window);
+      // TODO(antonm): accessing ports is not supported yet.
+  });
+}