Replaced Element.append with Node.appendChild

samples/third_party/dromaeo/tests/dom-modify-html.dart

 library dromaeo;
 import 'dart:async';
 import 'dart:html';
 import 'dart:json' as json;
 import 'dart:math' as Math;
 part 'Common.dart';
 part 'RunnerSuite.dart';
 
 void main() {
   final int num = 400;
@@ skipping 43 matching lines @@
     })
     .test('cloneNode', () {
       for (int i = 0; i < elems.length; i++) {
         ret = elems[i].clone(false);
         ret = elems[i].clone(true);
         ret = elems[i].clone(true);
         }
     })
     .test('appendChild', () {
       for (int i = 0; i < elems.length; i++)
-        document.body.$dom_appendChild(elems[i]);
+        document.body.append(elems[i]);
     })
     .test('insertBefore', () {
       for (int i = 0; i < elems.length; i++)
         document.body.insertBefore(elems[i], document.body.$dom_firstChild);
     })
     .end();
 }