To complete the tritych on companies transitioning to the mobile-centric future, here are some thoughts and facts about Google’s progress, or lack thereof: Despite Google’s mobile challenges, among web businesses it might be the biggest beneficiary so far of consumers’ shift to mobile devices. Google services are the top web property on smartphones, reaching 87 percent of the mobile audience through apps and mobile browsing, according to comScore. (Facebook is next with 85 percent.) And Google earned 42 percent of all mobile ad revenue in the United States last year, significantly more than any other company, according to eMarketer. Its share of mobile revenue, however, was down from 50 percent the year before and is not growing as quickly as that of Twitter, Apple and Facebook.