Remove "RenderBlock" class from examples that use it without giving it unrestricted height.

sky/tests/raw/box_layout.dart

 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
-import 'package:sky/rendering/block.dart';
 import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/object.dart';
 
 import '../resources/display_list.dart';
 
 void main() {
-  var size = new RenderConstrainedBox(additionalConstraints: new BoxConstraints().applyHeight(100.0));
-  var inner = new RenderDecoratedBox(decoration: new BoxDecoration(backgroundColor: const sky.Color(0xFF00FF00)), child: size);
-  var padding = new RenderPadding(padding: new EdgeDims.all(50.0), child: inner);
-  var block = new RenderBlock(children: [padding]);
-  var outer = new RenderDecoratedBox(decoration: new BoxDecoration(backgroundColor: const sky.Color(0xFF0000FF)), child: block);
+  RenderBox size = new RenderConstrainedBox(additionalConstraints: new BoxConstraints().applyHeight(100.0));
+  RenderBox inner = new RenderDecoratedBox(decoration: new BoxDecoration(backgroundColor: const sky.Color(0xFF00FF00)), child: size);
+  RenderBox padding = new RenderPadding(padding: new EdgeDims.all(50.0), child: inner);
+  RenderBox flex = new RenderFlex(children: [padding], direction: FlexDirection.vertical, alignItems: FlexAlignItems.stretch);
+  RenderBox outer = new RenderDecoratedBox(decoration: new BoxDecoration(backgroundColor: const sky.Color(0xFF0000FF)), child: flex);
   new TestRenderView(outer).endTest();
 }