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

sky/sdk/lib/framework/components2/drawer_header.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';
-import '../theme2/colors.dart';
-import '../theme2/view_configuration.dart';
-
-class DrawerHeader extends Component {
-
-  DrawerHeader({ Object key, this.children }) : super(key: key);
-
-  final List<UINode> children;
-
-  UINode build() {
-    return new Container(
-      height: kStatusBarHeight + kMaterialDrawerHeight,
-      decoration: new BoxDecoration(
-        backgroundColor: BlueGrey[50],
-        border: const Border(
-          bottom: const BorderSide(
-            color: const Color(0xFFD1D9E1),
-            width: 1.0
-          )
-        )
-      ),
-      padding: const EdgeDims.only(bottom: 7.0),
-      margin: const EdgeDims.only(bottom: 8.0),
-      child: new Flex([
-        new FlexExpandingChild(new Container(key: 'drawer-header-spacer')),
-        new Container(
-          key: 'drawer-header-label',
-          padding: const EdgeDims.symmetric(horizontal: 16.0),
-          child: new Flex(children, direction: FlexDirection.horizontal)
-        )],
-        direction: FlexDirection.vertical
-      )
-    );
-  }
-
-}