Add http://webstuff.nfshost.com/scrolling/ pageset

tools/perf/page_sets/tough_scrolling_cases/busy.js

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function busyLoop(millis) {
+    for (var d = Date.now(); Date.now() - d < millis; ) { }
+}
+
+function visible() {
+    if ("webkitVisibilityState" in document
+        && document.webkitVisibilityState == "hidden")
+        return false;
+    if ("mozVisibilityState" in document
+        && document.mozVisibilityState == "hidden")
+        return false;
+    if ("msVisibilityState" in document
+        && document.msVisibilityState == "hidden")
+        return false;
+    return true;
+}
+
+var timerId = 0;
+function loop() {
+    timerId = 0;
+    if (!visible())
+        return;
+    busyLoop(250);
+    timerId = window.setTimeout(loop, 50);
+}
+
+function handler() {
+    if (visible() && !timerId)
+        timerId = window.setTimeout(loop, 50);
+}
+
+document.addEventListener("webkitvisibilitychange", handler, false);
+document.addEventListener("mozvisibilitychange", handler, false);
+document.addEventListener("msvisibilitychange", handler, false);
+
+loop();