anchor.diff:        assert(_relayoutSubtreeRoot == this);
         RenderObject debugPreviousActiveLayout;
         assert(!_debugMutationsLocked);
  -      assert(!_debugDoingThisLayoutWithCallback);
  +      assert(!_doingThisLayoutWithCallback);
         assert(_debugCanParentUseSize != null);
         assert(() {
           _debugMutationsLocked = true;
  
positive.code:   void invokeLayoutCallback(LayoutCallback callback) {
      assert(_debugMutationsLocked);
      assert(_debugDoingThisLayout);
      assert(!_debugDoingThisLayoutWithCallback);
      assert(() {
        _debugDoingThisLayoutWithCallback = true;
        return true;
      });
      callback(constraints);
      assert(() {
        _debugDoingThisLayoutWithCallback = false;
        return true;
      });
    }
  
    // when the parent has rotated (e.g. when the screen has been turned
  
negative.code:     _constraints = constraints;
      _relayoutSubtreeRoot = relayoutSubtreeRoot;
      assert(!_debugMutationsLocked);
      assert(!_doingThisLayoutWithCallback);
      assert(() {
        _debugMutationsLocked = true;
        _debugCanParentUseSize = parentUsesSize;
  