Clean up how we remove nodes from the render tree, and make sure we reinsert them in the right plac…

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 'dart:async';
+
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/raised_button.dart';
+
+import '../resources/display_list.dart';
+
+class FiddleApp extends App {
+
+  bool arbitrarySetting = true;
+
+  void toggle() {
+    setState(() {
+      arbitrarySetting = !arbitrarySetting;
+    });
+  }
+
+  Widget buildFlex1() {
+    return new Flex([
+      new Flexible(child: new Container(
+        decoration: new BoxDecoration(
+          backgroundColor: const Color(0xFF00FFFF)
+        )
+      )),
+      new RaisedButton(child: new Text('TAP ME TO CHANGE THE BACKGROUND COLOUR'), onPressed: toggle)
+    ]);
+  }
+
+  Widget buildFlex2() {
+    return new Flex([
+      new Flexible(child: new Container(
+        key: 'something-else',
+        decoration: new BoxDecoration(
+          backgroundColor: const Color(0xEFFF9F00)
+        )
+      )),
+      new RaisedButton(child: new Text('PRESS ME TO CHANGE IT BACK'), onPressed: toggle)
+    ]);
+  }
+
+  Widget buildStack1() {
+    return new Stack([
+      new Positioned(child: new Container(
+        decoration: new BoxDecoration(
+          backgroundColor: const Color(0xFF00FFFF)
+        )
+      )),
+      new RaisedButton(child: new Text('TAP ME TO CHANGE THE BACKGROUND COLOUR'), onPressed: toggle)
+    ]);
+  }
+
+  Widget buildStack2() {
+    return new Stack([
+      new Positioned(child: new Container(
+        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()
+      )
+    ]);
+  }
+}
+
+main() {
+  TestRenderView renderViewOverride = new TestRenderView();
+  FiddleApp app = new FiddleApp();
+  runApp(app, renderViewOverride: renderViewOverride);
+  new Future.microtask(() {
+    renderViewOverride.checkFrame();
+    app.toggle();
+    new Future.microtask(() {
+      renderViewOverride.checkFrame();
+      app.toggle();
+      new Future.microtask(() {
+        renderViewOverride.checkFrame();
+        renderViewOverride.endTest();
+      });
+    });
+  });
+}