Cleanup isolate library after frog removal.

lib/isolate/dart2js/ports.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /** Common functionality to all send ports. */
 class _BaseSendPort implements SendPort {
   /** Id for the destination isolate. */
   final int _isolateId;
 
   const _BaseSendPort(this._isolateId);
@@ skipping 233 matching lines @@
     // map.getValues().forEach(_dispatch);
     map.getValues().forEach((e) => _dispatch(e));
   }
 
   visitSendPort(SendPort port) {
     if (port is _BufferingSendPort && port._port == null) {
       ports.add(port._futurePort);
     }
   }
 }