Make DifferenceEngine's markPatrolledLink and getRevisionHeader public so that hooked...

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