RFR: 8144075: Move prepare_for_oops_into_collection_set_do into pre_evacuate_collection_set

[Erik Helin]

Hi all,

this tiny patch just move the call to
g1_rem_set()->prepare_for_oops_into_collection_set_do() into
G1CollectedHeap::pre_evacuate_collection_set, instead of having it
in evacuate_collection_set. As the name of the method suggests,
prepare_for_oops_into_collection_set_do is more about preparation for
the evacuation than about the actual evacuation.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8144075

Webrev:
http://cr.openjdk.java.net/~ehelin/8144075/webrev.00/

Testing:
- GC test suite with full verification.

Thanks,
Erik