Rationalize Dart mojo and sky package structure

sky/sdk/lib/framework/layouts/block.dart

 
 import 'dart:sky' as sky;
 import '../fn.dart';
 
 class BlockLayout extends LayoutContainer {
 
   BlockLayout({
     Object key,
     List<UINode> children,
     Style style,
@@ skipping 10 matching lines @@
     skyNode.width = skyNode.parentNode.width;
     skyNode.getChildNodes().forEach((child) {
       child.layout();
       child.x = 0.0;
       child.y = y;
       y += child.height;
     });
     skyNode.height = y;
   }
 }