Expect to see William Shatner in some restaurant ads. Priceline on Friday reached an agreement to buy online reservation giant OpenTable for $2.6 billion in cash. The acquisition would move the popular travel-deal website into the restaurant business, and comes after acquisitions of Kayak and Booking.com. OpenTable claims it serves more than 15 million diners a month at more than 31,000 restaurants. Priceline agreed to pay $103 a share, a 46 percent premium on Thursday’s closing price.