Add UniqueComponent helper for creating components with unique states

packages/flutter/lib/src/fn3.dart

@@ -47,5 +47,6 @@ export 'fn3/theme.dart';
 export 'fn3/title.dart';
 export 'fn3/tool_bar.dart';
 export 'fn3/transitions.dart';
+export 'fn3/unique_component.dart';
 
 export 'package:vector_math/vector_math.dart' show Matrix4;

packages/flutter/lib/src/fn3/unique_component.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 'package:sky/src/fn3.dart';
+
+abstract class UniqueComponent<T extends State> extends StatefulComponent {
+ UniqueComponent({ GlobalKey key }) : super(key: key ?? new GlobalKey());
+
+ T createState();
+
+ T get currentState {
+   GlobalKey globalKey = key;
+   return globalKey.currentState;
+ }
+}