'Returns all fields values for a metric with a given name.
Args:
varname: Metric name.
Returns:
List of all fields values that were used for the specified metric. For
example, if there\'s a counter metric registered with fields
("renderer_type", int) and there were 2 calls to Increment:
Increment("renderer_type", fields=[1]),
Increment("renderer_type", fields=[2]), then
GetMetricFields("renderer_type") will return [(1,), (2,)].'

def GetMetricFields(self, varname):

    return self._metrics[varname].ListFieldsValues()
