Deprecate support for xhr.withCredentials for synchronous requests

LayoutTests/http/tests/xmlhttprequest/cross-origin-cookie-storage.html

 <button onclick="testSyncCookiesNoCredentials();">Start</button>
 <pre id="console"></pre>
 <script>
 if (window.testRunner) {
     testRunner.dumpAsText();
     testRunner.waitUntilDone();
     testRunner.setCanOpenWindows();
     testRunner.setAlwaysAcceptCookies(1);
 }
 
@@ skipping 82 matching lines @@
 
     clearCookies();
 
     var req = new XMLHttpRequest;
     req.open("GET", resourceURL("cross-origin-set-cookies.php"), false);
     req.withCredentials = true;
     req.send();
     log("PASS: Finished sync xhr.");
 
     var response = checkForCookie();
-    log(response.match(/WK\-xhr\-cookie\-storage: MySpecialValue/) ? "PASS: Cookie set." : "FAIL: no cookie set.");
+    // As per issue #383483 xhr.withCredentials for synchronous requests is deprecated. 
+    log(response.match(/WK\-xhr\-cookie\-storage: MySpecialValue/) ? "FAIL: Cookie set." : "PASS: no cookie set.");
     log("DONE");
     endTesting();
 }
 
 if (window.testRunner)
     testSyncCookiesNoCredentials();
 </script>