Move fn.dart into /sky/framework

sky/examples/fn/lib/fn.dart

-// 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';
-import 'dart:collection';
-import 'dart:sky' as sky;
-import 'reflect.dart' as reflect;
-
-part 'component.dart';
-part 'event.dart';
-part 'node.dart';
-part 'style.dart';
-
-bool _checkedMode;
-
-bool _debugWarnings() {
-  void testFn(double i) {}
-
-  if (_checkedMode == null) {
-    _checkedMode = false;
-    try {
-      testFn('not a double');
-    } catch (ex) {
-      _checkedMode = true;
-    }
-  }
-
-  return _checkedMode;
-}