List missing DLC in the properties window

[Kidofthecentury]

Probably has already been suggested (but I didn't find in the "already suggested" stickied thread), but how about listing all the DLCs available in the DLC tab in the game properties window with a "not owned" label?

So far quite a number of games (Railroad, Magicka to say two) have a high number of DLC and would be nice have a way to instantly check what those are missing.