'Subtracts all counters from the map.
For each counter in the passed map, subtracts its value to the counter in
this map.
Args:
counters_map: CounterMap instance to subtract.'

def sub_map(self, counters_map):

    for counter_name in counters_map.counters:
        self.increment(counter_name, (- counters_map.counters[counter_name]))
