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chromium/third_party/blink/perf_tests/css/PseudoClassSelectors.html 

<!DOCTYPE html>
<html>
<body>
<div id="test-target">
    <div>
        <div></div>
        <div>
            <p></p>
            <p></p>
            <p></p>
        </div>
        <div></div>
    </div>
    <div>
        <div>
            <p></p>
        </div>
    </div>
    <p></p>
    <p></p>
    <p></p>
    <p></p>
</div>
<script src="../resources/runner.js"></script>
<script>
PerfTestRunner.measureRunsPerSecond({
    description: "This benchmark tests CSS Selector performance with querySelector().",
    run: function() {
        for (var i = 0; i < 100; i++) {
            document.querySelector("p:first-child");
            document.querySelector("p:last-child");
            document.querySelector("p:first-of-type");
            document.querySelector("p:last-of-type");
            document.querySelector("p:nth-child(4n+3)");
            document.querySelector("p:nth-last-child(4n+3)");
            document.querySelector("p:nth-of-type(4n+3)");
            document.querySelector("p:nth-last-of-type(4n+3)");
        }
    }
});
</script>
</body>
</html>