Adding supported checks to media events

tests/html/media_stream_test.dart

 // Copyright (c) 2011, 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 media_stream_test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlIndividualConfiguration();
 
   group('supported', () {
     test('supported', () {
       expect(MediaStream.supported, true);
     });
   });
 
-  // No additional tests right now since this API prompts for user input to
-  // continue.
+  group('supported_MediaStreamEvent', () {
+    test('supported', () {
+      expect(MediaStreamEvent.supported, true);
+    });
+  });
+
+  group('supported_MediaStreamTrackEvent', () {
+    test('supported', () {
+      expect(MediaStreamTrackEvent.supported, true);
+    });
+  });
+
+  group('constructors', () {
+    test('MediaStreamEvent', () {
+      var expectation = MediaStreamEvent.supported ? returnsNormally : throws;
+      expect(() {
+        var event = document.$dom_createEvent('MediaStreamEvent');
+        expect(event is MediaStreamEvent, isTrue);
+      }, expectation);
+    });
+
+    test('MediaStreamTrackEvent', () {
+      var expectation =
+          MediaStreamTrackEvent.supported ? returnsNormally : throws;
+      expect(() {
+        var event = document.$dom_createEvent('MediaStreamTrackEvent');
+        expect(event is MediaStreamTrackEvent, isTrue);
+      }, expectation);
+    });
+  });
 }