anchor.diff:      assert(() {
         _debugActiveLayout = debugPreviousActiveLayout;
         _debugDoingThisLayout = false;
  -      _debugCanParentUseSize = null;
         _debugMutationsLocked = false;
         return true;
       });
  
positive.code:       RenderObject debugPreviousActiveLayout;
        assert(!_debugMutationsLocked);
        assert(!_debugDoingThisLayoutWithCallback);
        assert(() {
          _debugMutationsLocked = true;
          _debugCanParentUseSize = false;
          _debugDoingThisLayout = true;
          debugPreviousActiveLayout = _debugActiveLayout;
          _debugActiveLayout = this;
  
negative.code:       assert(() {
          _debugActiveLayout = debugPreviousActiveLayout;
          _debugDoingThisLayout = false;
          _debugMutationsLocked = false;
          return true;
        });
  