DifferenceEngine $mNewRev and $mOldRev are Revision objects (both protected variables) and the class is extended by lots of deployed extensions that access the variable
Uses in subclasses should be replaced with `getOldRevision` and `getNewRevision`, which return RevisionRecord
Extended by (in deployed extensions) - no uses remaining
[x] FlowBoardContentDiffView - no uses
[x] JCJsonDifferenceEngine - no uses
[x] MassMessageListDiffEngine - no uses
[x] NewsletterDiffEngine - no uses
[x] EntityContentDiffView - no uses
Have remaining uses:
[x] InlineDifferenceEngine
Non deployed extensions that access the variables:
[x] SocialProfile
[x] SpamDiffTool
Core update has merged, only thing remaining is to update Wikibase at https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/Wikibase/+/598858/