Block execution of failed 'crossorigin' <script>s.

LayoutTests/http/tests/security/script-crossorigin-loads-cross-origin.html

+<p>Test that a script element with a crossorigin attribute loads a cross-origin script correctly when the CORS check passes on the response.</p>
+<pre></pre>
+<script>
+if (window.testRunner) {
+    testRunner.dumpAsText();
+    testRunner.waitUntilDone();
+}
+
+var result = "FAIL";
+var have_reported = false;
+function loaded() {
+    if (!have_reported) {
+        document.querySelector("pre").innerHTML = result;
+        if (window.testRunner)
+            testRunner.notifyDone();
+        have_reported = true;
+    }
+}
+</script>
+<!-- This script should load -->
+<script crossorigin="anonymous" src="http://localhost:8000/security/resources/cors-script.php?cors=true&value=PASS" onload="loaded()"></script>
+<script>loaded();</script>