future: fix future.immediate allocator

corelib/src/implementation/future_implementation.dart

 // Copyright 2011 Google Inc. All Rights Reserved.
 // Dart core library.
 
 class FutureImpl<T> implements Future<T> {
 
   bool _isComplete;
 
   /**
    * Value that was provided to this Future by the Completer
    */
@@ skipping 18 matching lines @@
   /**
    * Exception handlers waiting for exceptions.
    */
   final List<Function> _exceptionHandlers;
 
   FutureImpl() : _listeners = new List(), _exceptionHandlers = new List() {
     _isComplete = false;
     _exceptionHandled = false;
   }
 
-  FutureImpl.immediate(T value) : this() {
-    _setValue(value);
+  factory FutureImpl.immediate(T value) {
+    final res = new FutureImpl();
+    res._setValue(value);
+    return res;
   }
 
   T get value() {
     if (!isComplete) {
       throw new FutureNotCompleteException();
     }
     if (_exception !== null) {
       throw _exception;
     }
     return _value;
@@ skipping 130 matching lines @@
   }
 
   void complete(T value) {
     _futureImpl._setValue(value);
   }
 
   void completeException(var exception) {
     _futureImpl._setException(exception);
   }
 }