The existing versionCollector metrics can tell us how many times various
metainfo endpoints are called, but they don't tell us how many bytes a
client is transferring. We currently can't collect precise information
on this, but we can collect information on how much planned traffic is
requested via order limits.
The implementation as provided is intended to measure objects sizes
before erasure encoding is taken into account.
Change-Id: I2f1d2a7831630e8439ecf5342e933df259151792
