Move dromaeo to third_party

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

 #library("dom-modify.dart");
 #import("dart:dom");
 #import('runner.dart');
 
 void main() {
   final int num = 400;
 
   String str = 'null';
   // Very ugly way to build up the string, but let's mimic JS version as much as possible.
   for (int i = 0; i < 1024; i++) {
@@ skipping 46 matching lines @@
     .test('appendChild', () {
       for (int i = 0; i < elems.length; i++)
         document.body.appendChild(elems[i]);
     })
     .test('insertBefore', () {
       for (int i = 0; i < elems.length; i++)
         document.body.insertBefore(elems[i], document.body.firstChild);
     })
     .end();
 }