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

sky/sdk/lib/framework/components2/tool_bar.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 '../rendering/flex.dart';
-import '../theme2/view_configuration.dart';
-import '../theme2/shadows.dart';
-
-class ToolBar extends Component {
-
-  ToolBar({
-    String key,
-    this.left,
-    this.center,
-    this.right,
-    this.backgroundColor
-  }) : super(key: key);
-
-  final UINode left;
-  final UINode center;
-  final List<UINode> right;
-  final Color backgroundColor;
-
-  UINode build() {
-    List<UINode> children = [
-      left,
-      new FlexExpandingChild(
-        new Padding(
-          child: center,
-          padding: new EdgeDims.only(left: 24.0)
-        ))
-    ];
-
-    if (right != null)
-      children.addAll(right);
-
-    return new Container(
-      child: new Flex(
-        [new Container(child: new Flex(children), height: kToolBarHeight)],
-        alignItems: FlexAlignItems.flexEnd
-      ),
-      padding: new EdgeDims.symmetric(horizontal: 8.0),
-      decoration: new BoxDecoration(
-        backgroundColor: backgroundColor,
-        boxShadow: Shadow[2]
-      )
-    );
-  }
-
-}