Bugfix in the inferrer for named optional parameter.

tests/language/inferrer_named_parameter_test.dart

+// Copyright (c) 2013, 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.
+
+// Regression test for dart2js's type inferrer, that used to not
+// correclty infer optional named parameters.
+
+import "package:expect/expect.dart";
+import "compiler_annotations.dart";
+
+@DontInline()
+foo({path}) {
+  () => 42;
+  return path;
+}
+
+main() {
+  foo(path: '42');
+  Expect.isFalse(foo() is String);
+}