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

sky/sdk/lib/framework/components2/icon.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';
-
-// TODO(eseidel): This should use package:.
-const String kAssetBase = '/packages/sky/assets/material-design-icons';
-
-class Icon extends Component {
-
-  Icon({
-    String key,
-    this.size,
-    this.type: ''
-  }) : super(key: key);
-
-  final int size;
-  final String type;
-
-  UINode build() {
-    String category = '';
-    String subtype = '';
-    List<String> parts = type.split('/');
-    if (parts.length == 2) {
-      category = parts[0];
-      subtype = parts[1];
-    }
-    return new Image(
-      size: new Size(size.toDouble(), size.toDouble()),
-      src: '${kAssetBase}/${category}/2x_web/ic_${subtype}_${size}dp.png'
-    );
-  }
-
-}