Even up here in the land of the actually free, police are starting to wear cameras (http://globalnews.ca/news/1093386/canadian-police-forces-looking-to-arm-officers-with-cameras/)
In my opinion, a camera on a cop is nothing more than an accurate, verifiable eye witness. It won't see or hear anything the officer won't already see and hear. Much better than an officer's memory and notebook.
Using google glasses... good. It won't provide any more information than the officer already has access to, or that can't be mined off a conventional camera's video. It may just provide the info quicker, when the officer needs it.
Maybe it's because I'm a white guy with a job. Maybe it's because I'm Canadian. But as a rule, I trust cops. Sure you get the odd bad cop, or a good cop making a mistake or having a bad day, but that happens with all people. Giving the cops a tool that provides information that might help reduce mistakes, and provides evidence both for and against them, to me is a good thing.