Three drawers: deli on top, crisper in the middle and locker at the bottom. The right-hand roller broke off the frame holding the bottom "Locker". The two wheels are still on the drawer itself.
So yes, the wheel that broke off was part of the frame, which mounts to the wall. (I'm not sure how it mounts.)
I'm looking on www.easyapplianceparts.com. Maybe I'm looking at the wrong thing. They show it as
Here's a link: http://www.easyapplianceparts.com/ModelFrames.aspx?ModelID=659414&ModelNum=KSRP25FSMS01&mfgModelNum=&ManufactureID=3&Selected=YOXKLEG7&Position=11&mfg=Whirlpool&Type=Appliance&Mark=11