Order the parameters of a function at the definition site.

tests/language/named_argument_test.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.
+
+main() {
+  var c1 = ({b, a}) => 'a: $a b: $b';
+  var c2 = ({a, b}) => 'a: $a b: $b';
+
+  Expect.equals ('a: 2 b: 1', c1(b: 1, a: 2));
+  Expect.equals ('a: 1 b: 2', c1(a: 1, b: 2));
+
+  Expect.equals ('a: 2 b: 1', c2(b: 1, a: 2));
+  Expect.equals ('a: 1 b: 2', c2(a: 1, b: 2));
+}