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

sky/tests/widgets/syncs1.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 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/raised_button.dart';
 
 import '../resources/display_list.dart';
 
 class FiddleApp extends App {
@@ skipping 46 matching lines @@
         key: 'something-else',
         decoration: new BoxDecoration(
           backgroundColor: const Color(0xEFFF9F00)
         )
       )),
       new RaisedButton(child: new Text('PRESS ME TO CHANGE IT BACK'), onPressed: toggle)
     ]);
   }
 
   Widget build() {
-    return new Block([
-      new SizedBox(
-        key: 'flex-example',
-        height: 250.0,
-        child: arbitrarySetting ? buildFlex1() : buildFlex2()
-      ),
-      new SizedBox(
-        key: 'stack-example',
-        height: 250.0,
-        child: arbitrarySetting ? buildStack1() : buildStack2()
-      )
-    ]);
+    return new Flex([
+        new SizedBox(
+          key: 'flex-example',
+          height: 250.0,
+          child: arbitrarySetting ? buildFlex1() : buildFlex2()
+        ),
+        new SizedBox(
+          key: 'stack-example',
+          height: 250.0,
+          child: arbitrarySetting ? buildStack1() : buildStack2()
+        )
+      ],
+      direction: FlexDirection.vertical,
+      alignItems: FlexAlignItems.stretch
+    );
   }
 }
 
 main() async {
   TestRenderView renderViewOverride = new TestRenderView();
   FiddleApp app = new FiddleApp();
   runApp(app, renderViewOverride: renderViewOverride);
   await renderViewOverride.checkFrame();
   app.toggle();
   await renderViewOverride.checkFrame();
   app.toggle();
   await renderViewOverride.checkFrame();
   renderViewOverride.endTest();
 }