Ping Pong Dim Sum, a modern Asian “tearoom” chain from London, is steaming across the Atlantic Ocean to open a Penn Quarter outlet next month. Its mélange of dumplings, sweet/savory small plates, flowering teas and trendy cocktails, served in swank surroundings, seems likely to score with Verizon Center ticket-holders, neighborhood denizens and visitors looking for a relatively inexpensive, yet upmarket, rest stop. Watch a dim sum demo from the restaurant above (900 Seventh St. NW).