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chromium/third_party/blink/web_tests/http/tests/preload/resources/media-link-headers.php 

<?php
    header("Link: <http://127.0.0.1:8000/resources/square.png?large>;rel=preload;as=image;media=\"(min-width: 300px)\"", false);
    header("Link: <http://127.0.0.1:8000/resources/square.png?small>;rel=preload;as=image;media=\"(max-width: 299px)\"", false);
?>
<!DOCTYPE html>
<meta name="viewport" content="width=160">
<script>
    window.addEventListener("load", function() {
        var entries = performance.getEntriesByType("resource");
        var smallLoaded = false;
        for (var i = 0; i < entries.length; ++i) {
            if (entries[i].name.indexOf("large") != -1)
                window.opener.postMessage("largeloaded", "*");
            if (entries[i].name.indexOf("small") != -1)
                smallLoaded = true;
        }
        if (smallLoaded)
            window.opener.postMessage("success", "*")
        window.opener.postMessage("smallnotloaded", "*");
    });
</script>
<script src="../resources/slow-script.pl?delay=200"></script>