By Christina Amann BERLIN, June 26 (Reuters) - Volkswagen is considering shutting four German factories and ramping up job cuts to as many as 100,000, two people familiar with the matter said on Friday, in what could be the biggest overhaul in the carmaker's history. Members of Volkswagen's supervisory board have been informed of the plans, which are due to be discussed at a July 9 meeting, the people said, as the carmaker faces mounting pressure from Chinese rivals.