Rationalize Dart mojo and sky package structure

sky/sdk/lib/framework/components/fixed_height_scrollable.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 '../animation/scroll_behavior.dart';
 import '../debug/tracing.dart';
 import '../fn.dart';
 import 'dart:math' as math;
 import 'dart:async';
 import 'scrollable.dart';
@@ skipping 86 matching lines @@
           style: _scrollAreaStyle,
           inlineStyle: transformStyle,
           children: buildItems(itemNumber, drawCount)
         )
       ]
     );
   }
 
   List<UINode> buildItems(int start, int count);  
 }