Fix Dromaeo performance tests.

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

 library dromaeo;
 import 'dart:async';
 import 'dart:html';
 import 'dart:json' as json;
 import '../common/common.dart';
 import 'dart:math' as Math;
 part 'Common.dart';
 part 'RunnerSuite.dart';
 
 
@@ skipping 23 matching lines @@
       document.body.append(div);
     })
     .test('firstChild', () {
       final nodes = document.body.$dom_childNodes;
       final nl = nodes.length;
 
       for (int i = 0; i < num; i++) {
         for (int j = 0; j < nl; j++) {
           Node cur = nodes[j];
           while (cur != null) {
-            cur = cur.$dom_firstChild;
+            cur = cur.firstChild;
           }
           ret = cur;
         }
       }
     })
     .test('lastChild', () {
       final nodes = document.body.$dom_childNodes;
       final nl = nodes.length;
 
       for (int i = 0; i < num; i++) {
         for (int j = 0; j < nl; j++) {
           Node cur = nodes[j];
           while (cur != null) {
-            cur = cur.$dom_lastChild;
+            cur = cur.lastChild;
           }
           ret = cur;
         }
       }
     })
     .test('nextSibling', () {
       for (int i = 0; i < num * 2; i++) {
-        Node cur = document.body.$dom_firstChild;
+        Node cur = document.body.firstChild;
         while (cur != null) {
           cur = cur.nextNode;
         }
         ret = cur;
       }
     })
     .test('previousSibling', () {
       for (int i = 0; i < num * 2; i++) {
-        Node cur = document.body.$dom_lastChild;
+        Node cur = document.body.lastChild;
         while (cur != null) {
           cur = cur.previousNode;
         }
         ret = cur;
       }
     })
     .test('childNodes', () {
       for (int i = 0; i < num; i++) {
         final nodes = document.body.$dom_childNodes;
         for (int j = 0; j < nodes.length; j++) {
           ret = nodes[j];
         }
       }
     })
     .end();
 }