The Giants are investing significant time this week in running backs. Coach Pat Shurmur’s enthusiasm for the position on Wednesday clearly was no joke. The Giants obviously seem interested in drafting one. Penn State back Saquon Barkley’s Thursday night interview with the Giants, it turns out, was only the tip of the iceberg. They also brought in N.C. State’s Nyheim Hines, as the Daily News first reported, and talked with USC’s Ronald Jones, LSU’s Derrius Guice, Auburn’s Kerryon Johnson, Mississippi’s Jordan Wilkins and San Diego State’s Rashaad Penny. Barkley, however, is considered by many scouts and analysts to be the best prospect in this entire draft, not just its best running back. And if the Cleveland Browns take a quarterback with the No. 1 overall pick, then Barkley would fall into the Giants’ laps and would be an obvious fit, especially because they’re scouting it as a prioritized need. So why, then, are the Giants doing so much homework on so many backs if a clear star in Barkley is theirs for the taking? They could be doing it for comparison’s sake, sure. Or hedging in case they are blown away by a quarterback they covet with the No. 2 pick. But there is another possible reason: the Browns might take Barkley themselves at one or trade the pick to another team that will. And the Giants need to be prepared if they do. Cleveland GM John Dorsey may have been posturing Thursday afternoon, granted, but he sounded like a man who wasn’t set on a quarterback yet, even though he knows the Browns need one.