Attempt to fix bug 1137717 by focusing the test frame

layout/base/tests/bug1132768-1.html

@@ -3,6 +3,7 @@
   <script src="/tests/SimpleTest/EventUtils.js"></script>
   <script>
     function test() {
+      focus();
       synthesizeMouseAtCenter(document.querySelector("span"), {});
     }
     function focused() {