sendBeacon should throw a TypeError on bad URLs.

third_party/WebKit/LayoutTests/svg/custom/tref-clone-crash.html

 <svg xmlns:xlink="http://www.w3.org/1999/xlink" onload="runTest()">
   <defs>
     <style id="style"/>
     <text id="ref"></text>
   </defs>
   <g><use xlink:href="#ref"/></g>
   <g><text><tref id="tref" xlink:href="#ref"/></text></g>
+  <script src="../../resources/gc.js"></script>
   <script>
-    function gc() {
-      if (window.GCController)
-        GCController.collect();
-      else {
-        for (var i = 0; i < 10000; ++i)
-          new Object;
-      }
-    }
     if (window.testRunner) {
       testRunner.dumpAsText();
       testRunner.waitUntilDone();
     }
     function runTest() {
       var tref = document.getElementById("tref");
       tref.cloneNode(true);
       gc();
       var elem = document.getElementById("style");
       var parent = elem.parentNode;
       parent.insertBefore(document.createElement("source"), elem);
       document.body.innerHTML = "PASS";
       if (window.testRunner)
         testRunner.notifyDone();
     }
   </script>
 </svg>