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chromium/third_party/blink/web_tests/http/tests/media/video-play-progress.html 

<!DOCTYPE html>
<title>Test that at least one progress event is fired after starting to load the video.</title>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<video></video>
<script>
async_test(function(t) {
    var video = document.querySelector("video");

    var watcher = new EventWatcher(t, video, ["loadstart", "progress"]);
    watcher.wait_for(["loadstart", "progress"]).then(t.step_func_done());

    var mediaFile = "resources/test.ogv";
    video.src = "http://127.0.0.1:8000/" + mediaFile;
    video.play();
  });
</script>