All users of this class use the same value for the latter 2 arguments.
MarkingNMethodClosure(OopClosure* cl, bool fix_relocations, bool keepalive_nmethods)

fix_relocations = false
keepalive_nmethods = true

Users:

G1FullGCMarkTask::work
PCAddThreadRootsMarkingTaskClosure
SerialFullGC::phase1_mark
ShenandoahSTWRootScanner::roots_do

Semantically, MarkingNMethodClosure can be used to identify live (on-stack) nmethods during full-gc marking, so no relocation should occur and encountered nmethods should be marked live. Therefore, these two bool args should have those values built in.