Adds basic sprite sheet support to sprites

sky/tests/resources/display_list.dart

 
 import 'dart:async';
 import 'dart:sky' as sky;
 import "dart:sky.internals" as internals;
 
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 
 typedef void Logger (String s);
@@ skipping 88 matching lines @@
   }
 
   void drawPath(Path path, Paint paint) {
     log("drawPath($path, $paint)");
   }
 
   void drawImage(sky.Image image, double x, double y, Paint paint) {
     log("drawImage($image, $x, $y, $paint)");
   }
 
+  void drawImageRect(sky.Image image, sky.Rect src, sky.Rect dst, Paint paint) {
+    log("drawImageRect($image, $src, $dst, paint)");
+  }
+
   void paintChild(RenderObject child, Point position) {
     log("paintChild ${child.runtimeType} at $position");
     child.paint(new TestDisplayList(width, height, logger, indent: "$indent  |"));
   }
 }
 
 class TestRenderView extends RenderView {
 
   TestRenderView([ RenderBox child = null ]) : super(child: child) {
     print("TestRenderView enabled");
@@ skipping 54 matching lines @@
 
   Future test(Function builder) {
     runApp(new TestApp(builder: builder), renderViewOverride: renderView);
     return renderView.checkFrame();
   }
 
   void endTest() {
     renderView.endTest();
   }
 }