Change to <- for types.

pkg/compiler/lib/src/enqueue.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.
 
 library dart2js.enqueue;
 
 import 'dart:collection' show Queue;
 
 import 'common/names.dart' show Identifiers;
 import 'common/resolution.dart' show Resolution;
@@ skipping 896 matching lines @@
   void visitStaticUse(StaticUse staticUse) {
     enqueuer.registerStaticUse(staticUse);
   }
 
   @override
   void visitTypeUse(TypeUse typeUse) {
     enqueuer.registerTypeUse(typeUse);
   }
 }
 
-typedef void _DeferredActionFunction();
-
 class _DeferredAction {
   final Element element;
-  final _DeferredActionFunction action;
+  final void<-() action;
 
   _DeferredAction(this.element, this.action);
 }