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chromium/third_party/blink/web_tests/media/controls-timeline.html 

<!DOCTYPE html>
<title>Test seeking on the media controls timeline</title>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<script src="media-controls.js"></script>
<video controls></video>
<script>
async_test(function(t) {
    var video = document.querySelector("video");
    video.src = "content/test.ogv";

    video.onloadedmetadata = t.step_func_done(function() {
        assert_equals(video.currentTime, 0);
        assert_equals(video.seeking, false);

        // click the middle of the timeline
        var coords = mediaControlsButtonCoordinates(video, "timeline");
        eventSender.mouseMoveTo(coords[0], coords[1]);
        eventSender.mouseDown();
        eventSender.mouseUp();

        var normalizedTime = video.currentTime / video.duration;
        assert_greater_than(normalizedTime, 0.4);
        assert_less_than(normalizedTime, 0.6);
        assert_equals(video.seeking, true);
    });
});
</script>