Add some tests to make sure message ports properly queue up message.

LayoutTests/http/tests/serviceworker/chromium/resources/postmessage-worker.js

 var port;
-var resultport = null;
-var result = null;
 
 self.onmessage = function(e) {
   var message = e.data;
   if ('port' in message) {
     port = message.port;
     port.onmessage = onMessage;
-  } else if ('done' in message) {
-    result = message.done;
-    if (resultport) {
-      resultport.postMessage(result);
-    }
-  } else if ('resultport' in message) {
-    resultport = message.resultport;
-    if (result) {
-      resultport.postMessage(result);
-    }
   }
 };
 
 function onMessage(e) {
   var message = e.data;
   if ('value' in message) {
     port.postMessage('Acking value: ' + message.value);
   } else if ('done' in message) {
     port.postMessage('quit');
   }
 }