Add cross-origin test with credentials.

tests/html/xhr_test.dart

Index: tests/html/xhr_test.dart
diff --git a/tests/html/xhr_test.dart b/tests/html/xhr_test.dart
index b5ea6c1cb0a1dfb6947581edf24f5e42d9311888..71ffebf8ac44ba565469145a48975646b643ab40 100644
--- a/tests/html/xhr_test.dart
+++ b/tests/html/xhr_test.dart
@@ -30,4 +30,12 @@ main() {
       expect(xhr.responseText, equals(''));
     }));
   });
+
+  test('XHR.getWithCredentials No file', () {
+    new HttpRequest.getWithCredentials("NonExistingFile", expectAsync1((xhr) {
+      expect(xhr.readyState, equals(HttpRequest.DONE));
+      expect(xhr.status, equals(0));
+      expect(xhr.responseText, equals(''));
+    }));
+  });
 }