Modified unittest to use new argument syntax.

tests/html/mutationobserver_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('mutationobserver_test');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 /**
@@ skipping 20 matching lines @@
           expect(nodes.length, count);
           expect(nodes, expectation);
         }
       }
 
       return expectAsyncUntil2(callback, () => done);
     }
 
     test('empty options is syntax error', () {
         var mutationObserver = new MutationObserver(
-            (mutations, observer) { expect(false, 'Should not be reached'); });
+            (mutations, observer) { expect(false, isTrue,
+                reason: 'Should not be reached'); });
         expect(() { mutationObserver.observe(document, {}); },
                throws);
       });
 
     test('direct-parallel options-map', () {
         var container = new DivElement();
         var div1 = new DivElement();
         var div2 = new DivElement();
         var mutationObserver = new MutationObserver(
             mutationCallback(2, orderedEquals([div1, div2])));
@@ skipping 47 matching lines @@
         var div2 = new DivElement();
         var mutationObserver = new MutationObserver(
             mutationCallback(2, orderedEquals([div1, div2])));
         mutationObserver.observe(container, childList: true, subtree: true);
 
         container.nodes.add(div1);
         div1.nodes.add(div2);
       });
   });
 }