Google Inc. opened a new social hub in its e-mail service on Tuesday, leaving little doubt that the Internet search leader is girding for a face-off with Facebook, reports the Associated Press. The new Gmail channel, called Google Buzz, includes many of the features that have turned Facebook into the Web’s top spot for fraternizing with friends and family. It comes less than a week after Facebook made changes of its own. Among other things, Facebook now shows a list of friends available for chatting on the left side of the page, similar to where Gmail now displays its chat feature. The Google Buzz features won’t reach all of Gmail’s estimated 176 million users worldwide for several more days. A link to the service will appear on the top left of the page, in a prominent position just under Gmail’s inbox tab…