The largest online ad industry trade group is pushing for new ad metrics to become standardized by the first quarter of 2013. The primary goal: begin to phase out reliance on the ad impressions-served metric and replace it with the viewable impressions metric. Also by that time the Interactive Advertising Bureau and its partners in the initiative expect advertisers and publishers will be using the eGRP metric, which industry players hope will complement the viewable impression metric with a more audience-focused gauge that speaks to brand advertisers. It was over a year ago that the IAB came together with The Association of National Advertisers and American Association of Advertising Agencies to introduce its sweeping…