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

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

Index: samples/third_party/dromaeo/tests/dom-modify-html.dart
===================================================================
--- samples/third_party/dromaeo/tests/dom-modify-html.dart	(revision 11181)
+++ samples/third_party/dromaeo/tests/dom-modify-html.dart	(working copy)
@@ -7,11 +7,12 @@
 
 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>[];