Joining the herd of Web sites jostling to cash in on the holiday shopping season, online search engine leader Google Inc. is adding a tool designed to make it easier for consumers to map out their local trips to the mall. The feature, to be unveiled Tuesday at Google's Froogle shopping site, will pinpoint the merchants selling a specific item within a designated ZIP code. Besides displaying a map showing all the local stores carrying the merchandise, Froogle also will list price differences.