Suggestion from David on the design doc (https://docs.google.com/document/d/1kLjnxPnBAX0G6W-3u6OF_VguuJc0pXdgCRVR0z3yn-g/edit#):

"If this class knows about the primary account, we can remove this parameter."

My response:

"We just need to make sure that the value that's passed from clients is always what IdentityManager would return."

That investigation would have to be done as part of making this change.