Refactor, rename, and generally rationalize code in the Frog isolates library,

lib/isolate/frog/ports.dart

Index: lib/isolate/frog/ports.dart
===================================================================
--- lib/isolate/frog/ports.dart	(revision 5269)
+++ lib/isolate/frog/ports.dart	(working copy)
@@ -92,6 +92,7 @@
 }
 
 /** A send port that delivers messages via worker.postMessage. */
+// TODO(eub): abstract this for iframes.
 class _WorkerSendPort extends _BaseSendPort implements SendPort {
   final int _workerId;
   final int _receivePortId;
@@ -110,9 +111,9 @@
 
       if (_globalState.isWorker) {
         // communication from one worker to another go through the main worker:
-        _globalState.mainWorker.postMessage(workerMessage);
+        _globalState.mainManager.postMessage(workerMessage);
       } else {
-        _globalState.workers[_workerId].postMessage(workerMessage);
+        _globalState.managers[_workerId].postMessage(workerMessage);
       }
     });
   }