If one spawns the following skeleton ~8-15 blocks y level above an iron golem at ground level (e.g:atop a small castle wall):

/summon skeleton ~ ~ ~ {HandItems:[{id:"minecraft:bow",Count:1b},{}],Attributes:[{Name:generic.followRange,Base:100}]}

Then the skeleton will sit endlessly on top of its perch until it is moved to a location within about 5 meters altitude of the Golem. It will then begin attacking the target.
This never happened in older versions of minecraft (although I can't provide exact versions, I used the attribute a lot) and really hampers map-making ability.

The followRange attribute seems rather buggy in general. In one instance, the skeleton targeted his enemy after being punched by me, in creative mode, and in another, a skeleton began pursuing one of the golems from a long distance, only to lose interest once he got close, possibly due to a small hill that was in his path.