FRIENDS told him not to do it. He'd even turned it down once already. The possible maelstrom of partisan controversy weighed on him. But in deciding to play the Decider for Oliver Stone's new satirical biopic, "W.," Josh Brolin relied on a very non-George W. Bush-like standard: doubt. Unlike the 43rd president of the United States, a man fatally confident of his actions, Brolin wasn't sure he could pull it off.