Scientists at a state animal health laboratory confirmed Monday that a popular brand of pet food submitted for testing by Marin veterinarians was indeed contaminated, even though it is not on a growing list of recalled pet foods. At the request of the Mill Valley Pet Clinic, three varieties of Nutro Max Cat Gourmet Classics, in 3-ounce cans, were tested by the California Animal Health and Food Safety Laboratory System at the University of California Davis School of Veterinary Medicine.