Add Stream.empty.

sdk/lib/async/future_impl.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.
 
 part of dart.async;
 
 /** The onValue and onError handlers return either a value or a future */
 typedef dynamic _FutureOnValue<T>(T value);
 /** Test used by [Future.catchError] to handle skip some errors. */
 typedef bool _FutureErrorTest(var error);
@@ skipping 215 matching lines @@
 
   Future<T> whenComplete(action()) {
     _Future result = new _Future<T>();
     if (!identical(result._zone, _ROOT_ZONE)) {
       action = result._zone.registerCallback(action);
     }
     _addListener(new _FutureListener.whenComplete(result, action));
     return result;
   }
 
-  Stream<T> asStream() => new Stream.fromFuture(this);
+  Stream<T> asStream() => new Stream<T>.fromFuture(this);
 
   void _markPendingCompletion() {
     if (!_mayComplete) throw new StateError("Future already completed");
     _state = _PENDING_COMPLETE;
   }
 
   T get _value {
     assert(_isComplete && _hasValue);
     return _resultOrListeners;
   }
@@ skipping 405 matching lines @@
       }
     }, onError: (e, s) {
       if (timer.isActive) {
         timer.cancel();
         result._completeError(e, s);
       }
     });
     return result;
   }
 }