Introduce Scaffold to Sky framework

sky/framework/components/scaffold.dart

Index: sky/framework/components/scaffold.dart
diff --git a/sky/framework/components/scaffold.dart b/sky/framework/components/scaffold.dart
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index 0000000000000000000000000000000000000000..60de2fb6850491748d0b8431cf0cec09d2e805a1
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+++ b/sky/framework/components/scaffold.dart
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+// 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 '../fn.dart';
+import 'action_bar.dart';
+import 'drawer.dart';
+import 'floating_action_button.dart';
+import 'package:sky/framework/theme/typography.dart' as typography;
+
+class Scaffold extends Component {
+  static final Style _style = new Style('''
+    ${typography.typeface};
+    ${typography.black.body1};''');
+
+  static final Style _mainStyle = new Style('''
+    display: flex;
+    flex-direction: column;
+    height: -webkit-fill-available;''');
+
+  static final Style _contentStyle = new Style('''
+    flex: 1;''');
+
+  static final Style _fabStyle = new Style('''
+    position: absolute;
+    bottom: 16px;
+    right: 16px;''');
+
+  static final Style _drawerStyle = new Style('''
+    position: absolute;
+    top: 0;
+    left: 0;
+    bottom: 0;
+    right: 0;''');
+
+  ActionBar actionBar;
+  Node content;
+  FloatingActionButton fab;
+  Drawer drawer;
+  List<Node> overlays;
+
+  Scaffold({
+    Object key,
+    this.actionBar,
+    this.content,
+    this.fab,
+    this.drawer,
+    this.overlays
+  }) : super(key: key);
+
+  Node build() {
+    var children = [
+      new Container(
+        key: 'Main',
+        style: _mainStyle,
+        children: [
+          actionBar,
+          new StyleNode(content, _contentStyle)
+        ]
+      ),
+    ];
+
+    if (fab != null)
+      children.add(new StyleNode(fab, _fabStyle));
+
+    if (drawer != null)
+      children.add(new StyleNode(drawer, _drawerStyle));
+
+    if (overlays != null)
+      children.addAll(overlays);
+
+    return new Container(style: _style, children: children);
+  }
+}