Retrieve the list of configured Google user accounts.

    Returns:
      list, the username strings of users congfigured by Google.

def GetConfiguredUsers(self):
    """Retrieve the list of configured Google user accounts.

    Returns:
      list, the username strings of users congfigured by Google.
    """
    if os.path.exists(self.google_users_file):
      users = open(self.google_users_file).readlines()
    else:
      users = []
    return [user.strip() for user in users]