Add initial framework for performance tests that measure frame rate.

chrome/test/data/perf/frame_rate/head.js

+// Copyright (c) 2011 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.
+
+var __running = false;
+var __old_title = "";
+var __scroll_by = 300;
+

[nduca, 2011/05/22 04:33:41]

Eg, on Nytimes (www/~nduca/test/perf/nytimes.html) i have this set up to
scrollBy 10. How do we customize this per page?

+var __t_last;
+var __t_est;
+var __t_est_total;
+var __t_est_squared_total;
+var __t_count;
+
+function __init_stats() {
+  __t_last = undefined;
+  __t_est = undefined;
+  __t_est_total = 0;
+  __t_est_squared_total = 0;
+  __t_count = 0;
+}
+__init_stats();
+
+function __calc_results() {
+  var M = __t_est_total / __t_count;
+  var X = __t_est_squared_total / __t_count;
+  var V = X - M * M;
+  var S = Math.sqrt(V);
+
+  var R = new Object();
+  R.mean = 1000.0 / M;
+  R.sigma = R.mean - 1000.0 / (M + S);
+  return R;
+}
+
+function __scroll_down() {
+  var y = window.scrollY;
+  window.scrollBy(0, __scroll_by);
+  if (window.scrollY == y)
+    __stop();
+}
+
+function __update_fps() {
+  var t_now = new Date().getTime();
+  if (window.__t_last) {
+    var t_delta = t_now - __t_last;
+    if (window.__t_est) {
+      __t_est = (0.1 * __t_est) + (0.9 * t_delta);  // low-pass filter
+    } else {
+      __t_est = t_delta;
+    }
+    var fps = 1000.0 / __t_est;
+    document.title = "FPS: " + (fps | 0);

[nduca, 2011/05/22 04:33:41]

avoid updating the title at all? Its not strictly needed, right?

+
+    __t_est_total += t_delta;
+    __t_est_squared_total += t_delta * t_delta;

[nduca, 2011/05/22 04:33:41]

Would be curious what the t_est_squared is on nytimes on chrome canary vs chrome
12. Not part of the review, but the answer might tell us how effective sigma is
here.

+    __t_count++;
+  }
+  __t_last = t_now;
+}
+
+function __sched_update() {
+  webkitRequestAnimationFrame(function() {

[nduca, 2011/05/22 04:33:41]

I think RAF passes in the frame begin time to the callback. That should give us
better results in the case our RAF runs after someone else's.

+    if (!__running)
+      return;
+    __update_fps();
+    __scroll_down();
+    __sched_update();
+  });
+}
+
+function __start() {

[nduca, 2011/05/22 04:33:41]

Maybe pass in scroll-by and some "am I done?" so that we can modify it per page?
No big deal.

+  if (__running)
+    return;
+  __old_title = document.title;
+  __running = true;
+  __sched_update();
+}
+
+function __stop() {
+  __running = false;
+  document.title = __old_title;
+}
+
+function __reset() {
+  __stop();
+  document.body.scrollTop = 0;
+  __init_stats();
+}
+
+function __force_compositor() {
+  document.body.style.webkitTransform = "translateZ(0)";
+}