Add typed wrapper functions to delegate classes.

lib/src/utils.dart

Index: lib/src/utils.dart
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0066003def2d4e8ce3482c2c8f338ddb29cd86f8
--- /dev/null
+++ b/lib/src/utils.dart
@@ -0,0 +1,7 @@
+// Copyright (c) 2016, 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.
+
+/// A generic typedef for a function that takes one type and returns another.
+typedef F UnaryFunction<E, F>(E argument);
+