Photo: Brex co-CEO Henrique Dubugras, Dropbox CEO Drew Houston and Splunk CEO Doug Merritt. Photos: BloombergSplunk, Dropbox and Brex followed similar formulas as they grew from small startups to established companies. To attract employees and customers, each set up elaborate San Francisco offices and plastered billboards for its services around the city. Dropbox three years ago leased a giant new office building on the city’s eastern edge. Fintech firm Brex even opened its own cafe in a neighborhood popular with venture capitalists.Now, all three companies embody a new trend: Their chief...…Photo: Brex co-CEO Henrique Dubugras, Dropbox CEO Drew Houston and Splunk CEO Doug Merritt. Photos: BloombergSplunk, Dropbox and Brex followed similar formulas as they grew from small startups to established companies. To attract employees and customers, each set up elaborate San Francisco offices and plastered billboards for its services around the city. Dropbox three years ago leased a giant new office building on the city’s eastern edge. Fintech firm Brex even opened its own cafe in a neighborhood popular with venture capitalists.Now, all three companies embody a new trend: Their chief...WW…