Have postMessage()s throw TypeError on failed arity checks.

LayoutTests/fast/workers/resources/worker-thread-multi-port.js

Index: LayoutTests/fast/workers/resources/worker-thread-multi-port.js
diff --git a/LayoutTests/fast/workers/resources/worker-thread-multi-port.js b/LayoutTests/fast/workers/resources/worker-thread-multi-port.js
index 6bed2ff502b0a97ed4b9302319b15780dd1434db..27424cc642c69052ce738aef00bbd78a08572ba9 100644
--- a/LayoutTests/fast/workers/resources/worker-thread-multi-port.js
+++ b/LayoutTests/fast/workers/resources/worker-thread-multi-port.js
@@ -26,6 +26,13 @@ onmessage = function(event) {
     } else if (event.data == "done") {
         postMessage("done");
         event.ports[0].postMessage("done");
+    } else if (event.data == "noargs") {
+        try {
+            postMessage();
+            testFailed("postMessage() did not throw");
+        } catch (e) {
+            testPassed("postMessage() threw exception: " + e);
+        }
     } else
         testFailed("Received unexpected message: " + event.data);
 };