After a change is created or updated using the 'cherry-pick'
functionality, this field will contain the source change number
and the patchset. Having this field helps us identify changes
where actual dev time was spent on by filtering out propagated
changes. This is especially useful for organizations wanting to
generate cost metrics.
Change-Id: I782a56aa52c52670ec74fabb713fe47ecba24de1
4a711eda84