As a step toward removing GC centric code from oop.hpp it would be nice to replace oop_ps_push_contents with calls to oop_iterate with a GC specific closure.

This is number one in a series of three enhancements to remove Parallel GC specific code from shared code
JDK-8201436
JDK-8211446
JDK-8211447

Similar work has been done in the past, but the ParallelGC visitor functions have not been converted yet.

See previous work in this area:
JDK-8138737: Remove oop_ms_adjust_pointers and use oop_iterate instead
JDK-8129417: Oop iteration clean-up to remove oop_ms_follow_contents