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chromium/third_party/blink/web_tests/http/tests/cookies/same-site/popup-same-site-post.https.html 

<!doctype html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/cookies/resources/testharness-helpers.js"></script>
<body>
<script>
if (window.location.hostname == "127.0.0.1") {
    window.location.hostname = ORIGINAL_HOST;
} else if (window.location.hostname == ORIGINAL_HOST) {
    async_test(t => {
        clearKnownCookies();
        document.cookie = STRICT_DOM + "=1; SameSite=Strict; Max-Age=100; path=/";
        document.cookie = LAX_DOM + "=1; SameSite=Lax; Max-Age=100; path=/";
        document.cookie = UNSPECIFIED_DOM + "=1; Max-Age=100; path=/";
        // SameSite=None cookies must be Secure.
        document.cookie = NONE_DOM + "=1; SameSite=None; Secure; Max-Age=100; path=/";

        window.addEventListener("message", t.step_func_done(e => {
            assert_equals(e.data.http[STRICT_DOM], "1", "strict");
            assert_equals(e.data.http[LAX_DOM], "1", "lax");
            assert_equals(e.data.http[UNSPECIFIED_DOM], "1", "unspecified");
            assert_equals(e.data.http[NONE_DOM], "1", "none");
            assert_equals(e.data.document, STRICT_DOM + "=1; " + LAX_DOM + "=1; " + UNSPECIFIED_DOM + "=1; " + NONE_DOM + "=1");
            e.source.close();
        }));

        var f = document.createElement('form');
        f.action = "https://" + ORIGINAL_HOST + ":8443/cookies/resources/post-cookies-to-opener.php";
        f.method = "POST";
        f.target = "_blank";
        f.rel = "opener";
        window.onload = t.step_func(f.submit.bind(f));
        document.body.appendChild(f);
    }, "'" + ORIGINAL_HOST + "' is same-site with itself, so samesite cookies are sent.");
}
</script>
</body>