Adding test for bug 5374

tests/html/xhr_test.dart

 // 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 XHRTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 import 'dart:json' as json;
 
@@ skipping 33 matching lines @@
     });
 
     test('XHR file', () {
       var xhr = new HttpRequest();
       xhr.open('GET', url, true);
       xhr.on.readyStateChange.add(expectAsyncUntil1((e) {
         if (xhr.readyState == HttpRequest.DONE) {
           validate200Response(xhr);
         }
       }, () => xhr.readyState == HttpRequest.DONE));
+
+      xhr.onLoadEnd.listen(expectAsync1((ProgressEvent e) {
+        expect(e.currentTarget, xhr);
+        expect(e.target, xhr);
+      }));
       xhr.send();
     });
 
     test('XHR.get No file', () {
       new HttpRequest.get("NonExistingFile", expectAsync1((xhr) {
         expect(xhr.readyState, equals(HttpRequest.DONE));
         validate404(xhr);
       }));
     });
 
@@ skipping 21 matching lines @@
     test('HttpRequestProgressEvent', () {
       var expectation = HttpRequestProgressEvent.supported ?
           returnsNormally : throws;
       expect(() {
         var event = new Event.eventType('XMLHttpRequestProgressEvent', '');
         expect(event is HttpRequestProgressEvent, isTrue);
       }, expectation);
     });
   });
 }