The fate of the proposed Chicago home for the Lucas Museum of Narrative Art, the brainchild of George Lucas, a name associated with futuristic images, may hinge on a legal principle as old as ancient Rome.The four-count lawsuit filed in November by the nonprofit Friends of the Parks organization is based exclusively on the public trust doctrine. Whether this historic doctrine will prevent the construction of the museum will likely be decided early next year. By court order, discovery in the case is scheduled to close on …