Move example fn widgets into sky/framework/components

sky/framework/components/fixed_height_scrollable.dart

-part of widgets;
+// 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 '../animation/fling-curve.dart';
+import '../fn.dart';
+import 'dart:sky' as sky;
 
 abstract class FixedHeightScrollable extends Component {
-
   // TODO(rafaelw): This component really shouldn't have an opinion
   // about how it is sized. The owning component should decide whether
   // it's explicitly sized or flexible or whatever...
-  static Style _style = new Style('''
+  static final Style _style = new Style('''
     overflow: hidden;
     position: relative;
     flex: 1;
     will-change: transform;'''
   );
 
-  static Style _scrollAreaStyle = new Style('''
+  static final Style _scrollAreaStyle = new Style('''
     position:relative;
     will-change: transform;'''
   );
 
   double minOffset;
   double maxOffset;
 
   double _scrollOffset = 0.0;
   FlingCurve _flingCurve;
   int _flingAnimationId;
   double _height = 0.0;
   double _itemHeight;
 
   FixedHeightScrollable({
     Object key,
     this.minOffset,
     this.maxOffset
-  }) : super(key: key) {}
+  }) : super(key: key) {
+    events.listen('gestureflingstart', _handleFlingStart);
+    events.listen('gestureflingcancel', _handleFlingCancel);
+    events.listen('gesturescrollupdate', _handleScrollUpdate);
+    events.listen('wheel', _handleWheel);
+  }
 
   List<Node> buildItems(int start, int count);
 
   void didMount() {
     var root = getRoot();
     var item = root.firstChild.firstChild;
     sky.ClientRect scrollRect = root.getBoundingClientRect();
     sky.ClientRect itemRect = item.getBoundingClientRect();
     assert(scrollRect.height > 0);
     assert(itemRect.height > 0);
@@ skipping 25 matching lines @@
 
     return new Container(
       style: _style,
       children: [
         new Container(
           style: _scrollAreaStyle,
           inlineStyle: transformStyle,
           children: buildItems(itemNumber, drawCount)
         )
       ]
-    )
-    ..events.listen('gestureflingstart', _handleFlingStart)
-    ..events.listen('gestureflingcancel', _handleFlingCancel)
-    ..events.listen('gesturescrollupdate', _handleScrollUpdate)
-    ..events.listen('wheel', _handleWheel);
+    );
   }
 
   void didUnmount() {
     _stopFling();
   }
 
   bool _scrollBy(double scrollDelta) {
     var newScrollOffset = _scrollOffset + scrollDelta;
     if (minOffset != null && newScrollOffset < minOffset) {
       newScrollOffset = minOffset;
@@ skipping 43 matching lines @@
   }
 
   void _handleFlingCancel(sky.GestureEvent event) {
     _stopFling();
   }
 
   void _handleWheel(sky.WheelEvent event) {
     _scrollBy(-event.offsetY);
   }
 }