Bug 854421 - Part 11: Use rAF instead of setTimeout in a test. r=roc

layout/generic/test/test_bug633762.html

@@ -35,8 +35,8 @@ function runTests() {
   scrollTopBefore = doc.body.scrollTop;
   // send up arrow key event
   sendKey("UP");
-
-  setTimeout("finish();", 20);
+  
+  window.requestAnimationFrame(finish);
 }
 
 function finish() {