Clean up some Dart idioms in fn

sky/examples/fn/lib/fn.dart

Index: sky/examples/fn/lib/fn.dart
diff --git a/sky/examples/fn/lib/fn.dart b/sky/examples/fn/lib/fn.dart
index 30ec0408a60f215e07ec29752fca74dacb3f1f92..ab67c50bd603100390886d90813cdf4a45a07916 100644
--- a/sky/examples/fn/lib/fn.dart
+++ b/sky/examples/fn/lib/fn.dart
@@ -1,3 +1,7 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
 library fn;
 
 import 'dart:async';
@@ -11,7 +15,7 @@ part 'style.dart';
 
 bool _checkedMode;
 
-bool debugWarnings() {
+bool _debugWarnings() {
   void testFn(double i) {}
 
   if (_checkedMode == null) {