Make changing themes work again.

sky/sdk/lib/widgets/widget.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 'dart:collection';
 import 'dart:sky' as sky;
 
 import 'package:sky/base/debug.dart';
 import 'package:sky/base/hit_test.dart';
@@ skipping 188 matching lines @@
     }
 
     assert(oldNode == null || (oldNode.mounted == false && oldNode.parent == null));
     assert(!newNode.mounted);
     newNode.setParent(this);
     newNode._sync(oldNode, slot);
     assert(newNode.root is RenderObject);
     return newNode;
   }
 
+  String _adjustPrefixWithParentCheck(Widget child, String prefix) {
+    if (child.parent == this)
+      return prefix;
+    if (child.parent == null)
+      return '$prefix [[DISCONNECTED]] ';
+    return '$prefix [[PARENT IS ${child.parent.toStringName()}]] ';
+  }
+
   String toString([String prefix = '', String startPrefix = '']) {
     String childrenString = '';
     List<Widget> children = new List<Widget>();
     walkChildren(children.add);
     if (children.length > 0) {
       Widget lastChild = children.removeLast();
       String nextStartPrefix = prefix + ' +-';
       String nextPrefix = prefix + ' | ';
       for (Widget child in children)
-        childrenString += child.toString(nextPrefix, nextStartPrefix);
-      String lastStartPrefix = prefix + ' \'-';
-      String lastPrefix = prefix + '   ';
-      childrenString += lastChild.toString(lastPrefix, lastStartPrefix);
+        childrenString += child.toString(nextPrefix, _adjustPrefixWithParentCheck(child, nextStartPrefix));
+      nextStartPrefix = prefix + ' \'-';
+      nextPrefix = prefix + '   ';
+      childrenString += lastChild.toString(nextPrefix, _adjustPrefixWithParentCheck(lastChild, nextStartPrefix));
     }
     return '$startPrefix${toStringName()}\n$childrenString';
   }
   String toStringName() {
     if (key == null)
       return '$runtimeType(unkeyed; hashCode=$hashCode)';
     return '$runtimeType("$key"; hashCode=$hashCode)';
   }
 
 }
@@ skipping 303 matching lines @@
   bool retainStatefulNodeIfPossible(StatefulComponent newNode) {
     assert(!_disqualifiedFromEverAppearingAgain);
     assert(newNode != null);
     assert(runtimeType == newNode.runtimeType);
     assert(key == newNode.key);
     assert(_built != null);
     newNode._disqualifiedFromEverAppearingAgain = true;
 
     newNode._built = _built;
     _built = null;
-
-    syncFields(newNode);
     _dirty = true;
 
     return true;
   }
 
+  // because our retainStatefulNodeIfPossible() method returns true,
+  // when _sync is called, our 'old' is actually the new instance that
+  // we are to copy state from.
   void _sync(Widget old, dynamic slot) {
     assert(!_disqualifiedFromEverAppearingAgain);
     // TODO(ianh): _sync should only be called once when old == null
     if (old == null && !_isStateInitialized) {
       initState();
       _isStateInitialized = true;
     }
+    if (old != null)
+      syncFields(old);
     super._sync(old, slot);
   }
 
   // Stateful components can override initState if they want
   // to do non-trivial work to initialize state. This is
   // always called before build().
   void initState() { }
 
-  // This is called by retainStatefulNodeIfPossible(), during
-  // syncChild(), just before _sync() is called. Derived
-  // classes should override this method to update `this` to
-  // account for the new values the parent passed to `source`.
-  // Make sure to call super.syncFields(source) unless you are
-  // extending StatefulComponent directly.
+  // This is called by _sync(). Derived classes should override this
+  // method to update `this` to account for the new values the parent
+  // passed to `source`. Make sure to call super.syncFields(source)
+  // unless you are extending StatefulComponent directly.
   void syncFields(Component source);
 
   Widget syncChild(Widget node, Widget oldNode, dynamic slot) {
     assert(!_disqualifiedFromEverAppearingAgain);
     return super.syncChild(node, oldNode, slot);
   }
 
   void setState(Function fn()) {
     assert(!_disqualifiedFromEverAppearingAgain);
     fn();
@@ skipping 507 matching lines @@
 }
 
 class AppContainer extends AbstractWidgetRoot {
   AppContainer(this.app) {
     assert(SkyBinding.instance is WidgetSkyBinding);
   }
   final App app;
   Widget build() => new RenderViewWrapper(child: app);
 }
 
+AppContainer _container;
 void runApp(App app, { RenderView renderViewOverride, bool enableProfilingLoop: false }) {
   WidgetSkyBinding.initWidgetSkyBinding(renderViewOverride: renderViewOverride);
-  new AppContainer(app);
+  _container = new AppContainer(app);
   if (enableProfilingLoop) {
     new Timer.periodic(const Duration(milliseconds: 20), (_) {
       app.scheduleBuild();
     });
   }
 }
+void debugDumpApp() {
+  if (_container != null)
+    _container.toString().split('\n').forEach(print);
+  else
+    print("runApp() not yet called");
+}
+
 
 class RenderBoxToWidgetAdapter extends AbstractWidgetRoot {
 
   RenderBoxToWidgetAdapter(
     RenderObjectWithChildMixin<RenderBox> container,
     this.builder
   ) : _container = container, super() {
     assert(builder != null);
   }
 
@@ skipping 21 matching lines @@
     if (root.parent == null) {
       // we haven't attached it yet
       assert(_container.child == null);
       _container.child = root;
     }
     assert(root.parent == _container);
   }
 
   Widget build() => builder();
 }