Make dart2js Isolate.spawn work.

sdk/lib/isolate/isolate.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.
 
 /**
  * Concurrent programming using _isolates_:
  * independent workers that are similar to threads
  * but don't share memory,
  * communicating only via messages.
  *
@@ skipping 12 matching lines @@
   // TODO(floitsch): clean up spawn exception.
   const IsolateSpawnException(String this._s);
   String toString() => "IsolateSpawnException: '$_s'";
   final String _s;
 }
 
 class Isolate {
 
   final SendPort _controlPort;
 
-  Isolate._fromControlPort(this._controlPort);
+  Isolate.fromControlPort(SendPort controlPort)
+      : this._controlPort = controlPort;
 
   /**
    * Creates and spawns an isolate that shares the same code as the current
    * isolate.
    *
    * The argument [entryPoint] specifies the entry point of the spawned
    * isolate. It must be a static top-level function or a static method that
    * takes no arguments. It is not allowed to pass a function closure.
    *
    * The entry-point function is invoked with the initial [message].
@@ skipping 47 matching lines @@
    * The content of [message] can be: primitive values (null, num, bool, double,
    * String), instances of [SendPort], and lists and maps whose elements are any
    * of these. List and maps are also allowed to be cyclic.
    *
    * In the special circumstances when two isolates share the same code and are
    * running in the same process (e.g. isolates created via [spawnFunction]), it
    * is also possible to send object instances (which would be copied in the
    * process). This is currently only supported by the dartvm.  For now, the
    * dart2js compiler only supports the restricted messages described above.
    *
-   * The second argument [replyTo] is deprecated.
+   * The second argument [replyTo] is deprecated and its value is ignored.
    */
   void send(var message, [SendPort replyTo]);
 
   /**
    * Tests whether [other] is a [SendPort] pointing to the same
    * [ReceivePort] as this one.
    */
   bool operator==(var other);
 
   /**
@@ skipping 119 matching lines @@
   const IsolateUnhandledException(this.message, this.source, this.stackTrace);
 
   String toString() {
     return 'IsolateUnhandledException: exception while handling message: '
         '${message} \n  '
         '${source.toString().replaceAll("\n", "\n  ")}\n'
         'original stack trace:\n  '
         '${stackTrace.toString().replaceAll("\n","\n  ")}';
   }
 }