Summary:
This collects the highest round in which a label adds a fetch, as well as
number of fetches per label per datasource. It reports these, along with
aggregated values with scuba sample of profiling data.
Aggregation for number of rounds is the maximum round of label or any of
label's children. Aggregation for number of fetches is sum.
Reviewed By: simonmar
Differential Revision: D3316018
fbshipit-source-id: 152690c7b8811d22f566437675c943f755029528
