SendPort + ReceivePort changes:

lib/isolate/frog/isolateimpl.dart

Index: lib/isolate/frog/isolateimpl.dart
diff --git a/lib/isolate/frog/isolateimpl.dart b/lib/isolate/frog/isolateimpl.dart
index 09fb97d3812954e55c7ecf53497ba23adff89081..84ff343ec77ad6d5d5102d710ef1ef5666bdd8ca 100644
--- a/lib/isolate/frog/isolateimpl.dart
+++ b/lib/isolate/frog/isolateimpl.dart
@@ -308,8 +308,9 @@ class _IsolateNatives {
   /** JavaScript-specific implementation to spawn an isolate. */
   static Future<SendPort> spawn(Isolate isolate, bool isLight) {
     Completer<SendPort> completer = new Completer<SendPort>();
-    ReceivePort port = new ReceivePort.singleShot();
+    ReceivePort port = new ReceivePort();
     port.receive((msg, SendPort replyPort) {
+      port.close();
       assert(msg == _SPAWNED_SIGNAL);
       completer.complete(replyPort);
     });
@@ -558,8 +559,9 @@ class _IsolateNatives {
 
   static _spawn2(String functionName, String uri, bool isLight) {
     Completer<SendPort> completer = new Completer<SendPort>();
-    ReceivePort port = new ReceivePort.singleShot();
+    ReceivePort port = new ReceivePort();
     port.receive((msg, SendPort replyPort) {
+      port.close();
       assert(msg == _SPAWNED_SIGNAL);
       completer.complete(replyPort);
     });