first-scroll-runs-on-compositor.html

<!DOCTYPE HTML>
<script src="../../../../resources/testharness.js"></script>
<script src="../../../../resources/testharnessreport.js"></script>
<script src="scroll-animation.js"></script>
<title>The first programmatic smooth scroll runs on compositor</title>
<style>
body {
    width: 2000px;
    height: 2000px;
}
</style>
<script>
// From ScrollAnimatorCompositorCoordinator::RunState
var RUNNING_ON_COMPOSITOR = "RunningOnCompositor";
var RUNNING_ON_MAIN_THREAD = "RunningOnMainThread";

function waitForCompositor() {
  return new Promise((resolve, reject) => {
    function tick(frames) {
      if (frames >= 10 ||
          internals.getProgrammaticScrollAnimationState(document) ==
          RUNNING_ON_MAIN_THREAD) {
        reject("First scroll ran on main thread.");
      }
      if (internals.getProgrammaticScrollAnimationState(document) ==
          RUNNING_ON_COMPOSITOR) {
        resolve();
      }
      requestAnimationFrame(tick.bind(null, frames + 1));
    }

    if (!window.internals)
      reject("This test requires window.internals.");
    tick(0);
  });
}

requestAnimationFrame(() => {
promise_test(t => {
  document.scrollingElement.scrollTop = 0;
  window.scrollBy({top: 500, behavior: "smooth"});
  return waitForCompositor()
        .then(waitForWindowScrollEnd.bind(this, '', 500))
        .then(() => {
            assert_approx_equals(document.scrollingElement.scrollTop, 500, 1);
        });
    }, "The first programmatic smooth scroll doesn't always run on the main " +
       "thread (see crbug.com/592799).");
});
</script>
chromium/third_party/blink/web_tests/virtual/threaded-prefer-compositing/fast/scroll-behavior/first-scroll-runs-on-compositor.html
