Add property base to the Uri class

tests/html/uri_test.dart

-// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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 mouse_event_test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
 
-  test('relatedTarget', () {
-    var event = new MouseEvent('mouseout');
-    expect(event.relatedTarget, isNull);
+  test('Uri.base', () {
+    expect(Uri.base.scheme, "http");
+    expect(Uri.base.toString(), window.location.href);
   });
 }