Add RenderClip and use it in FixedHeightScrollable

sky/sdk/lib/framework/fn2.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.
 
 library fn;
 
 import 'app.dart';
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors';
@@ skipping 334 matching lines @@
     super.removeChild(node);
   }
 
   void _remove() {
     if (child != null)
       removeChild(child);
     super._remove();
   }
 }
 
+class Clip extends OneChildRenderObjectWrapper {
+  RenderClip root;
+
+  Clip({ UINode child, Object key })
+    : super(child: child, key: key);
+
+  RenderClip createNode() => new RenderClip();
+}
+
 class Padding extends OneChildRenderObjectWrapper {
   RenderPadding root;
   final EdgeDims padding;
 
   Padding({ this.padding, UINode child, Object key })
     : super(child: child, key: key);
 
   RenderPadding createNode() => new RenderPadding(padding: padding);
 
   void syncRenderObject(Padding old) {
@@ skipping 589 matching lines @@
     assert(root.parent is RenderView);
   }
 }
 
 class Text extends Component {
   Text(this.data) : super(key: '*text*');
   final String data;
   bool get interchangeable => true;
   UINode build() => new Paragraph(text: data);
 }