anchor.diff:    DecoratedType visitTopLevelVariableDeclaration(
         TopLevelVariableDeclaration node) {
       node.metadata.accept(this);
  -    _createFlowAnalysis(null);
  +    _createFlowAnalysis(null, null);
       try {
         node.variables.accept(this);
       } finally {
  +      _flowAnalysis.finish();
         _flowAnalysis = null;
       }
       return null;
  
positive.code:           action: () => node.functionExpression.body.accept(this));
      } finally {
        _currentFunctionType = null;
        _flowAnalysis = null;
      }
      return null;
  
negative.code:     for (var variable in node.variables) {
        variable.metadata.accept(this);
        var initializer = variable.initializer;
        _flowAnalysis.add(variable.declaredElement,
            assigned: initializer != null);
        if (initializer != null) {
          var destinationType = getOrComputeElementType(variable.declaredElement);
          if (typeAnnotation == null) {
  