anchor.diff:      super._buildIfDirty();
     }
   
  -  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;
  -    }
  -    super._sync(old, slot);
  -  }
  -
  -  Widget syncChild(Widget node, Widget oldNode, dynamic slot) {
  -    assert(!_disqualifiedFromEverAppearingAgain);
  -    return super.syncChild(node, oldNode, slot);
  -  }
  -
     bool retainStatefulNodeIfPossible(StatefulComponent newNode) {
       assert(!_disqualifiedFromEverAppearingAgain);
       assert(newNode != null);
  
positive.code:     return true;
    }
  
    // This is called by retainStatefulNodeIfPossible(), during
    // syncChild(), just before _sync() is called. Derived
    // classes should override this method to update `this` to
  
negative.code:   // 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);
  