Fix up Performance testing.

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;
-import 'dart:json' as json;
 part 'Common.dart';
 part 'RunnerSuite.dart';
 
 
 void main() {
   final int num = 40;
 
   // Try to force real results.
   var ret;
 
@@ skipping 65 matching lines @@
     .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();
 }