docs: def HandleWellKnownFlows(self, messages):
      """Hands off messages to well known flows."""
      msgs_by_wkf = {}
      result = []
      for msg in messages:
        # Regular message - queue it.
        if msg.response_id != 0:
          result.append(msg)
          continue
  
        # Well known flows:
        flow_name = msg.session_id.FlowName()
  
        if flow_name in self.well_known_flows:
          # This message should be processed directly on the front end.
          msgs_by_wkf.setdefault(flow_name, []).append(msg)
  
          # TODO(user): Deprecate in favor of 'well_known_flow_requests'
          # metric.
          stats_collector_instance.Get().IncrementCounter(
              "grr_well_known_flow_requests")
  
          stats_collector_instance.Get().IncrementCounter(
              "well_known_flow_requests", fields=[str(msg.session_id)])
        else:
          # Message should be queued to be processed in the backend.
  
          # Well known flows have a response_id==0, but if we queue up the state
          # as that it will overwrite some other message that is queued. So we
          # change it to a random number here.
          msg.response_id = random.UInt32()
  
          # Queue the message in the data store.
          result.append(msg)
  
      for flow_name, msg_list in iteritems(msgs_by_wkf):
        wkf = self.well_known_flows[flow_name]
        wkf.ProcessMessages(msg_list)
  
      return result