Private libraries used.

sdk/lib/_internal/compiler/implementation/lib/isolate_patch.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.
 
 // Patch file for the dart:isolate library.
 
+import 'dart:_isolate_helper' show IsolateNatives,
+                                   lazyPort,
+                                   ReceivePortImpl;
+
 patch class _Isolate {
   patch ReceivePort get port {
     if (lazyPort == null) {
       lazyPort = new ReceivePort();
     }
     return lazyPort;
   }
 
   patch SendPort spawnFunction(void topLevelFunction(),
       [bool UnhandledExceptionCallback(IsolateUnhandledException e)]) {
     return IsolateNatives.spawnFunction(topLevelFunction);
   }
 
   patch SendPort spawnUri(String uri) {
     return IsolateNatives.spawn(null, uri, false);
   }
 }
 
 /** Default factory for receive ports. */
 patch class ReceivePort {
   patch factory ReceivePort() {
     return new ReceivePortImpl();
   }
 }