Add very basic MessageEventTest.

client/tests/client/dom/MessageEventTest.dart

Index: client/tests/client/dom/MessageEventTest.dart
diff --git a/client/tests/client/dom/MessageEventTest.dart b/client/tests/client/dom/MessageEventTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4a6aed0cff873b9f09330107d24585008b05417a
--- /dev/null
+++ b/client/tests/client/dom/MessageEventTest.dart
@@ -0,0 +1,22 @@
+#library('SerializedScriptValueTest');
+#import('../../../../lib/unittest/unittest.dart');
+#import('../../../../lib/unittest/dom_config.dart');
+#import('dart:dom');
+
+main() {
+  useDomConfiguration();
+
+  test('MessageEvent.initMessageEvent', () {
+      final event = document.createEvent('MessageEvent');
+      event.initMessageEvent('type', false, true, 'data', 'origin', 'lastEventId', window, []);
+      expect(event.type).equals('type');
+      expect(event.bubbles).equals(false);
+      expect(event.cancelable).equals(true);
+      expect(event.data).equals('data');
+      expect(event.origin).equals('origin');
+      expect(event.lastEventId).equals('lastEventId');
+      // TODO(antonm): add identical to Expectation.
+      Expect.identical(window, event.source);
+      // TODO(antonm): accessing ports is not supported yet.
+  });
+}