McKesson Corp. exists in the shadows, but it’s not shady. Unlike a lot of California tech giants, the San Francisco-based healthcare company does not seek attention, either by spouting off about its greatness or whining about the state’s difficult business environment. In fact, even though it has the second highest revenues of any California company (Apple is first), you’ve probably never heard of McKesson. Zocalo Public Square columnist Joe Mathews finds that refreshing. He’s especially impressed by McKesson’s longevity in a state that often lavishes its attentions on start-ups that crash and burn in short order.