Refactor fn2.dart, since it breached our 1000-line threshold.

sky/sdk/lib/framework/components2/modal_overlay.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.
-
-import '../fn2.dart';
-
-class ModalOverlay extends Component {
-
-  ModalOverlay({ Object key, this.children, this.onDismiss }) : super(key: key);
-
-  // static final Style _style = new Style('''
-  //   position: absolute;
-  //   top: 0;
-  //   left: 0;
-  //   bottom: 0;
-  //   right: 0;''');
-
-  final List<UINode> children;
-  final GestureEventListener onDismiss;
-
-  UINode build() {
-    return new EventListenerNode(
-      new Stack(children),
-      onGestureTap: onDismiss);
-  }
-
-}