code: def add_group_email_grant(self, permission, email_address, headers=None):
          
          acl = self.get_acl(headers=headers)
          acl.add_group_email_grant(permission, email_address)
          self.set_acl(acl, headers=headers)
docs: Convenience method that provides a quick way to add an email group
          grant to a key. This method retrieves the current ACL, creates a new
          grant based on the parameters passed in, adds that grant to the ACL and
          then PUT's the new ACL back to GS.
  
          :type permission: string
          :param permission: The permission being granted. Should be one of:
              READ|FULL_CONTROL
              See http://code.google.com/apis/storage/docs/developer-guide.html#authorization
              for more details on permissions.
  
          :type email_address: string
          :param email_address: The email address associated with the Google
              Group to which you are granting the permission.