As a child, Savina Darzes would wander down to the San Francisco wharf near the Ghirardelli Chocolate Factory. The scent of chocolate wafted over the piers, mixing with sea salt and the noise of the docks. Little wonder that when Ms. Darzes grew up and moved to Portland, she organized a gourmet twist on the old-fashioned sightseeing tour with the Portland Chocolate Walking and Tasting Tours.