'Registers a counter metric (integer value that never decreases).
Args:
varname: Metric name.
fields: Metric dimensions. For example, "renderer_latency" metric may
have "renderer_name" dimension. Fields are provided as list of
tuples, like: [("renderer_name", string)].
docstring: Metric description.
units: Metric units (see stats.MetricUnits for details).
If metric with the same name was registered before, it will be overwritten.'

@utils.Synchronized
def RegisterCounterMetric(self, varname, fields=None, docstring=None, units=None):

    self._metrics[varname] = _CounterMetric(fields, docstring, units)
    self._metrics_metadata[varname] = MetricMetadata(varname=varname, metric_type=MetricMetadata.MetricType.COUNTER, value_type=MetricMetadata.ValueType.INT, fields_defs=self.FieldsToFieldsDefinitions(fields), docstring=docstring, units=units)
