Add CORS support for <link> elements.

LayoutTests/http/tests/security/resources/link-crossorigin-common.js

+// Tiny test rig for all security/link-crossorigin-*.html tests,
+// which exercise <link> + CORS variations.
+if (window.testRunner) {
+    testRunner.dumpAsText();
+    testRunner.waitUntilDone();
+}
+
+// The common case is to have four sub-tests. To override
+// for a test, assign window.test_count.
+var default_test_count = 4;
+
+var event_count = 0;
+test_count = window.test_count || default_test_count;
+
+function finish(pass, msg) {
+    var out = document.querySelector("pre");
+    var txt = pass ? "PASS" : "FAIL";
+    if (msg) txt += ": " + msg;
+    out.appendChild(document.createTextNode(txt));
+    out.appendChild(document.createElement("br"));
+    if (++event_count >= test_count && window.testRunner)
+        testRunner.notifyDone();
+}
+
+function pass() { finish(true); }
+function fail() { finish(false); }