Merge "- fix the AccountManager documentation. http://b/2401790 - only pass...

Merge "- fix the AccountManager documentation. http://b/2401790 - only pass the authtoken through from the authenticator to the client   for getAuthToken() and strip it out from the other calls, like   addAccount(). http://b/2332762 - beef up the documentation to indicate what calls are allowed to be made   from the main thread and which are not allowed. http://b/2384961 - wait a bit before retrying syncs that failed because one was already   in progress. http://b/2414235"