Remove AsyncError with Expando.

runtime/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.
 
 class _CloseToken {
   /// This token is sent from [IsolateSink]s to [IsolateStream]s to ask them to
   /// close themselves.
   const _CloseToken();
 }
 
@@ skipping 16 matching lines @@
 
 class _IsolateSink implements IsolateSink {
   bool _isClosed = false;
   final SendPort _port;
   _IsolateSink._fromPort(this._port);
 
   void add(dynamic message) {
     _port.send(message);
   }
 
-  void addError(AsyncError errorEvent) {
-    throw new UnimplementedError("signalError on isolate streams");
+  void addError(Object errorEvent) {
+    throw new UnimplementedError("addError on isolate streams");
   }
 
   void close() {
     if (_isClosed) return;
     add(const _CloseToken());
     _isClosed = true;
   }
 
   bool operator==(var other) {
     return other is IsolateSink && _port == other._port;
@@ skipping 137 matching lines @@
     }
     return _portInternal;
   }
 
   /* patch */ static spawnFunction(void topLevelFunction(),
       [bool unhandledExceptionCallback(IsolateUnhandledException e)])
       native "isolate_spawnFunction";
 
   /* patch */ static spawnUri(String uri) native "isolate_spawnUri";
 }