Make rendering use PaintingNodes for increased efficiency.

sky/tests/resources/display_list.dart

 
 import 'dart:async';
 import 'dart:sky' as sky;
 import 'dart:typed_data';
 
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 
 import 'harness.dart';
 
 typedef void Logger (String s);
 
 class TestPaintingCanvas extends PaintingCanvas {
   TestPaintingCanvas(sky.PictureRecorder recorder, Size size, this.logger, { this.indent: '' })
     : size = size,
-      super(recorder, size) {
+      super(recorder, Point.origin & size) {
     log("TestPaintingCanvas() constructor: ${size.width} x ${size.height}");
   }
 
   final String indent;
   final Size size;
 
   Logger logger;
   void log(String s) {
     logger("${indent} ${s}");
   }
@@ skipping 151 matching lines @@
 
   Future test(Function builder) {
     runApp(new TestApp(builder: builder), renderViewOverride: renderView);
     return renderView.checkFrame();
   }
 
   void endTest() {
     renderView.endTest();
   }
 }