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

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

+<p>Test that a script element with a crossorigin attribute does not load a cross-origin script when the resource sharing check fails on the response.</p>
+<pre></pre>
+<script>
+if (window.testRunner) {
+    testRunner.dumpAsText();
+    testRunner.waitUntilDone();
+}
+
+var result = "PASS";
+
+function must_not_fire() {
+    result = "FAIL";
+}
+
+function finish() {
+    document.querySelector("pre").innerHTML = result;
+    if (window.testRunner)
+        testRunner.notifyDone();
+}
+</script>
+<!-- This script should _not_ load, nor fire onload. -->
+<script crossorigin="anonymous" src="http://localhost:8000/security/resources/cors-script.php?cors=false&value=FAIL" onload="must_not_fire()" onerror="finish();"></script>