third_party/web_platform_tests/FileAPI/progress-manual.html

<!DOCTYPE html>
<meta charset=utf-8>
<title>Process Events for FileReader</title>
<link rel=help href="http://dev.w3.org/2006/webapi/FileAPI/#event-handler-attributes-section">
<link rel=author title="Jinks Zhao" href="mailto:jinks@maxthon.com">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
Please choose one file through this input below.<br>
<input type="file" id="filer">
<div id="log"></div>
<script>
var input, reader, progressEventCounter, progressEventTimeList,
    lastProgressEventTime;
setup(function() {
    input = document.getElementById('filer');
    reader = new FileReader();
    progressEventCounter = 0;
    progressEventTimeList = [];
    lastProgressEventTime;
}, { explicit_timeout: true });

var t = async_test("FileReader progress events.")

reader.onprogress = t.step_func(function () {
    var newTime = new Date;
    var timeout = newTime - lastProgressEventTime;

    progressEventTimeList.push(timeout);
    lastProgressEventTime = newTime;
    progressEventCounter++;

    assert_less_than_equal(timeout, 50, "The progress event should be fired every 50ms.");
});

reader.onload = t.step_func_done(function () {
    assert_greater_than_equal(progressEventCounter, 1,
                              "When read completely, the progress event must be fired at least once.")
});

input.onchange = t.step_func(function () {
    var files = input.files;

    assert_greater_than(files.length, 0);
    var file = files[0];

    lastProgressEventTime = new Date;
    reader.readAsArrayBuffer(file);
});
</script>