EBay Inc. is buying rapidly growing online ticket broker StubHub Inc. for $310 million in cash, further expanding the Internet auctioneer's electronic bazaar. The San Jose-based company announced the deal late Wednesday after the news had already been leaked to the media. StubHub's sale, expected to close before April, punctuates another improbable Internet success story. Jeff Fluhr, StubHub's 32-year-old co-founder and chief executive, launched the San Francisco startup against the dreary backdrop of the dot-com bust 6 1/2 years ago with another former student at Stanford Graduate School of Business, Eric Baker. "StubHub's business model is an excellent fit with...