anchor.diff:      for (var parameter in formals) {
         var declaration = makeVariableDeclaration(parameter.element,
             initializer: parameter is DefaultFormalParameter
  -              ? buildOptionalExpression(parameter.defaultValue)
  +              ? buildOptionalTopLevelExpression(parameter.defaultValue)
                 : null,
             type: buildType(parameter.element.type));
         switch (parameter.kind) {
  
positive.code:             isAsync: body.isAsynchronous, isStar: body.isGenerator));
    }
  
    ast.Expression buildTopLevelExpression(Expression node) {
      try {
        return _expressionBuilder.build(node);
  
negative.code:   }
  
    ast.Initializer buildInitializer(ConstructorInitializer node) {
      try {
        return new InitializerBuilder(this).build(node);
      } on _CompilationError catch (_) {
        return new ast.InvalidInitializer();
      }
    }
  
    bool isFinal(Element element) {
  