Move dromaeo to third_party

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

 #library("dom-attr.dart");
 #import("dart:dom");
 #import('runner.dart');
 
 void main() {
   final int num = 10240;
 
   // Try to force real results.
   var ret;
 
@@ skipping 12 matching lines @@
     .test('setAttribute', () {
         for (int i = 0; i < num; i++)
         a.setAttribute('id', 'foo');
     })
     .test('element.property = value', () {
       for (int i = 0; i < num; i++)
         a.id = 'foo';
     })
     .end();
 }