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chromium/third_party/blink/perf_tests/xml_http_request/send.html 

<!DOCTYPE html>
<script src="../resources/runner.js"></script>
<script>
// Use measureTime instead of runsPerSecond to avoid a ridiculous number of requests in flight.
// 100 is realistic, 1000 is plausible, but 10000 is crazy.
PerfTestRunner.measureTime({
    description: "Measure the time it takes to create, open, and send 1000 async XMLHttpRequests",
    run: function() {
        var xhrs = [];
        for (var i = 0; i < 1000; ++i) {
            var xhr = new XMLHttpRequest();
            xhr.open("GET", "file" + i + ".txt", true);
            xhr.send();
            xhrs.push(xhr);
        }
    },
});
</script>