President Barack Obama is back in town tomorrow for some pre-Halloween Hollywood trick-or-treats courtesy of J.J. Abrams and the Tinseltown ATM. In a whirlwind 6 1/2-hour visit to Los Angeles on Saturday, the fundraiser-in-chief will hit a trio of deep-pocket events — which means, of course, there will be traffic snarls and road closures all over the city’s Westside (see the full list of closures from LAPD below). After landing at LAX around 1 PM, Obama heads over to the…