Expose diff IDs to post-diff workflows.
Expose diff IDs to post-diff workflows.

Summary:

Test Plan:

Reviewers:

CC:

wharris/arcanist,alexmv/arcanist,wharris/arcanist,Khan/arcanist,wharris/arcanist,hach-que/arcanist,dguo-coursera/arcanist,phacility/arcanist,haskell-infra/arcanist,codelabs-ch/arcanist,eSpark/arcanist,folsom-labs/arcanist,jra3/arcanist,sneakpeeq/arcanist,codelabs-ch/arcanist,chundongwang/arcanist,calblueprint/arcanist,zhihu/arcanist,memsql/arcanist,Symplicity/arcanist,Khan/arcanist,alexmv/arcanist,zhihu/arcanist,KieranHayes/arcanist,eSpark/arcanist,folsom-labs/arcanist,r4nt/arcanist,wxstars/arcanist,coursera/arcanist,dguo-coursera/arcanist,Symplicity/arcanist,hach-que/arcanist,folsom-labs/arcanist,wxstars/arcanist,sneakpeeq/arcanist,haskell-infra/arcanist,codelabs-ch/arcanist,eSpark/arcanist,PageUpPeopleOrg/arcanist-patches,phacility/arcanist,chundongwang/arcanist,aik099/arcanist,wikimedia/phabricator-arcanist,zhihu/arcanist,calblueprint/arcanist,fivestars/arcanist,eSpark/arcanist,chundongwang/arcanist,memsql/arcanist,PageUpPeopleOrg/arcanist-patches,kevinseelbach/arcanist,r4nt/arcanist,calblueprint/arcanist,uber/arcanist,aik099/arcanist,uber/arcanist,coursera/arcanist,kevinseelbach/arcanist,jra3/arcanist,hach-que/arcanist,KieranHayes/arcanist,aik099/arcanist,jra3/arcanist,alexmv/arcanist,wxstars/arcanist,zhihu/arcanist,sneakpeeq/arcanist,wharris/arcanist,KieranHayes/arcanist,coursera/arcanist,kevinseelbach/arcanist,Symplicity/arcanist,Khan/arcanist,memsql/arcanist,dguo-coursera/arcanist,wikimedia/phabricator-arcanist,wikimedia/phabricator-arcanist,jra3/arcanist,KieranHayes/arcanist,Symplicity/arcanist,uber/arcanist,phacility/arcanist,phacility/arcanist,fivestars/arcanist,julkiewicz/arcanist,haskell-infra/arcanist,Khan/arcanist,kevinseelbach/arcanist,phacility/arcanist,uber/arcanist,coursera/arcanist,r4nt/arcanist,sneakpeeq/arcanist,r4nt/arcanist,chundongwang/arcanist,codelabs-ch/arcanist,dguo-coursera/arcanist,wikimedia/phabricator-arcanist,julkiewicz/arcanist,haskell-infra/arcanist,PageUpPeopleOrg/arcanist-patches,wxstars/arcanist,julkiewicz/arcanist,hach-que/arcanist,fivestars/arcanist,calblueprint/arcanist,aik099/arcanist,julkiewicz/arcanist,folsom-labs/arcanist,memsql/arcanist,PageUpPeopleOrg/arcanist-patches,codelabs-ch/arcanist,fivestars/arcanist,alexmv/arcanist