By Julie Jargon, Dow Jones Newswires Chipotle Mexican Grill Inc. has a new problem: poor customer service. The burrito chain, battered by disease outbreaks last year, says cleanliness in its restaurants and speed of service have suffered as a result of a new focus on food safety. Co-CEO Steve Ells says the company is now focusing with “laserlike” attention on those problems to draw customers back.