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chromium/third_party/blink/web_tests/media/media-can-load-when-hidden.html 

<!DOCTYPE html>
<title>Test HTMLMediaElement to be sure that the video is getting loaded even if the element is hidden.</title>
<style>
    video { display: none; }
</style>
<video></video>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<script>
async_test(function(t) {
    var video = document.querySelector("video");
    video.ondurationchange = t.step_func_done();
    video.src = "content/test.ogv";
});
</script>