function createVariableStatement(listOrBinding,
                                        identifier = undefined,
                                        initializer = undefined) {
  if (listOrBinding instanceof VariableDeclarationList)
    return new VariableStatement(null, listOrBinding);
  let binding = listOrBinding;
  let list = createVariableDeclarationList(binding, identifier, initializer);
  return createVariableStatement(list);
}
@param {VariableDeclarationList|TokenType} listOrBinding
@param {string|IdentifierToken=} identifier
@param {ParseTree=} initializer
@return {VariableStatement}