This isn't the same as the ones an app has been currently granted - that might be a subset of the ones it would like in total.
This shows how to get the currently granted set. Before Android M, that's the full set because it wouldn't have been installed unless the user had granted all of the ones it wanted. Under Android M however, the user can choose which to grant, and change at any time after installation. I'd like the full set an app would like as listed in it's manifest.