Returns counts of flow results grouped by result type.

def CountFlowResultsByType(self, client_id, flow_id):
    """Returns counts of flow results grouped by result type."""
    result = collections.Counter()
    for hr in self.ReadFlowResults(client_id, flow_id, 0, sys.maxsize):
      key = compatibility.GetName(hr.payload.__class__)
      result[key] += 1

    return result