Make dart2js Isolate.spawn work.

sdk/lib/isolate/isolate.dart

Index: sdk/lib/isolate/isolate.dart
diff --git a/sdk/lib/isolate/isolate.dart b/sdk/lib/isolate/isolate.dart
index 1ee77d736294fb267755cc0ee5f1ef5afb1ae9b5..e688a722c967d94917780c24eb605825f319a55f 100644
--- a/sdk/lib/isolate/isolate.dart
+++ b/sdk/lib/isolate/isolate.dart
@@ -30,7 +30,8 @@ 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
@@ -98,7 +99,7 @@ abstract class SendPort {
    * 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]);