Make DifferenceEngine's markPatrolledLink and getRevisionHeader public so that hooked functions can use them where needed
The said hooks were added to core in
https://gerrit.wikimedia.org/r/#/c/298026/ . One of the many intended use
cases is https://gerrit.wikimedia.org/r/#/c/326074/ which currently fatals
due to these two being protected, and obviously we don't want to lose
functionality when hooking into one (or more) of the aforementioned hooks.
Change-Id: I260c8b57c0bb2af3a6982bd7142b112a4a023391
Depends-On: I02de9069854532faec4c0c1798a10f862e6dfd7c