Make dart2js Isolate.spawn work.

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.
 
 patch class ReceivePort {
   /* patch */ factory ReceivePort() = _ReceivePortImpl;
 
   /* patch */ factory ReceivePort.fromRawReceivePort(RawReceivePort rawPort) =
       _ReceivePortImpl.fromRawReceivePort;
 }
@@ skipping 176 matching lines @@
   /* patch */ static Future<Isolate> spawn(
       void entryPoint(message), var message) {
     Completer completer = new Completer<Isolate>.sync();
     try {
       // The VM will invoke [_startIsolate] with entryPoint as argument.
       SendPort controlPort = _Isolate._spawnFunction(entryPoint);
       RawReceivePort readyPort = new RawReceivePort();
       controlPort.send([message, readyPort.sendPort]);
       readyPort.handler = (_) {
         readyPort.close();
-        completer.complete(new Isolate._fromControlPort(controlPort));
+        completer.complete(new Isolate.fromControlPort(controlPort));
       };
     } catch(e, st) {
       // TODO(floitsch): we want errors to go into the returned future.
       rethrow;
     };
     return completer.future;
   }
 
   /* patch */ static Future<Isolate> spawnUri(Uri uri, var message) {
     Completer completer = new Completer<Isolate>.sync();
     try {
       // The VM will invoke [_startIsolate].
       SendPort controlPort = _Isolate._spawnUri(uri.path);
       RawReceivePort readyPort = new RawReceivePort();
       controlPort.send([message, readyPort.sendPort]);
       readyPort.handler = (_) {
         readyPort.close();
-        completer.complete(new Isolate._fromControlPort(controlPort));
+        completer.complete(new Isolate.fromControlPort(controlPort));
       };
     } catch(e, st) {
       // TODO(floitsch): we want errors to go into the returned future.
       rethrow;
     };
     return completer.future;
   }
 }
 
 patch class _Isolate {
   /* patch */ static ReceivePort get port {
     if (_portInternal == null) {
       _portInternal = new ReceivePort.fromRawReceivePort(_getPortInternal());
     }
     return _portInternal;
   }
 
   static SendPort _spawnFunction(Function topLevelFunction)
       native "isolate_spawnFunction";
 
   /* patch */ static SendPort _spawnUri(String uri) native "isolate_spawnUri";
 }