Wraps AggregationFactory to report additional measurements.

The function measurement_fn is a python callable that will be called on value (if inner_agg_factory is an UnweightedAggregationFactory) or (value, weight) (if inner_agg_factory is a WeightedAggregationFactory) in the next function of the AggregationProcess produced by the returned factory to generate additional measurements. It must be traceable by TFF and expect tff.Value objects placed at CLIENTS as inputs, and return collections.OrderedDicts mapping string names to tensor values placed at SERVER, which will be added to the measurement dict produced by the inner_agg_factory.

inner_agg_factory The factory to wrap and add measurements.
measurement_fn A python callable that will be called on value (and/or weight) provided to the next function to compute additional measurements.

An AggregationFactory that reports additional measurements.