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

LayoutTests/fast/events/resources/message-port-multi.js

 if (window.testRunner) {
     testRunner.dumpAsText();
     testRunner.waitUntilDone();
 }
 
 description("This test checks the various use cases around sending multiple ports through MessagePort.postMessage");
 
 var channel = new MessageChannel();
 var channel2 = new MessageChannel();
 var channel3 = new MessageChannel();
 var channel4 = new MessageChannel();
 
+shouldThrow("channel.port1.postMessage()");
+
 channel.port1.postMessage("noport");
 channel.port1.postMessage("zero ports", []);
 channel.port1.postMessage("two ports", [channel2.port1, channel2.port2]);
 
 // Now test various failure cases
 shouldThrow('channel.port1.postMessage("same port", [channel.port1])', '"DataCloneError: Failed to execute \'postMessage\' on \'MessagePort\': Port at index 0 contains the source port."');
 shouldThrow('channel.port1.postMessage("null port", [channel3.port1, null, channel3.port2])', '"TypeError: Failed to execute \'postMessage\' on \'MessagePort\': Value at index 1 is an untransferable \'null\' value."');
 shouldThrow('channel.port1.postMessage("notAPort", [channel3.port1, {}, channel3.port2])', '"TypeError: Failed to execute \'postMessage\' on \'MessagePort\': Value at index 1 does not have a transferable type."');
 shouldThrow('channel.port1.postMessage("duplicate port", [channel3.port1, channel3.port1])', '"DataCloneError: Failed to execute \'postMessage\' on \'MessagePort\': Message port at index 1 is a duplicate of an earlier port."');
 // Should be OK to send channel3.port1 (should not have been disentangled by the previous failed calls).
@@ skipping 115 matching lines @@
     } else if (event.data == "entangled ports") {
         if (event.ports.length == 2)
             testPassed("event.ports contains two ports when two ports re-sent after error");
         else
             testFailed("event.ports contained " + event.ports.length + " when two ports re-sent after error");
     } else if (event.data == "done") {
         testTransfers();
     } else
         testFailed("Received unexpected message: " + event.data);
 }