Fix up Dromaeo tests for the removal of the Math.random call.

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

 #library("dom_modify_html");
 #import("dart:html");
 #import("dart:json");
 #import("dart:math", prefix: "Math");
 #source("Common.dart");
 #source("RunnerSuite.dart");
 
 void main() {
   final int num = 400;
+  var random = new Math.Random();
 
   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++) {
-    str = "$str${new String.fromCharCodes([((25 * Math.random()) + 97).toInt()])}";
+    str = "$str${new String.fromCharCodes([((25 * random.nextDouble()) + 97).toInt()])}";
   }
 
   List<Node> elems = <Node>[];
 
   // Try to force real results.
   var ret;
 
   final htmlstr = document.body.innerHTML;
 
   new Suite(window, 'dom-modify')
@@ skipping 35 matching lines @@
     .test('appendChild', () {
       for (int i = 0; i < elems.length; i++)
         document.body.$dom_appendChild(elems[i]);
     })
     .test('insertBefore', () {
       for (int i = 0; i < elems.length; i++)
         document.body.insertBefore(elems[i], document.body.$dom_firstChild);
     })
     .end();
 }