RFR (S): 8138750: Clean up survivor rate group

[Thomas Schatzl]

Hi all,

  can I have reviews for the following cleanup (read deletion) of unused
code and some better naming/moving it to a better place for some method?

In particular:
- Surv_rate_group::accum_surv_rate() is never called, so remove it and
all code referencing _accum_surv_rate.
- CollectorState has this method

 124   bool should_propagate() const { // XXX should have a more
suitable state name or abstraction for this

that is only used for updating the survivor rate group predictors in the
collector policy. Since it does not have anything to do with G1
collector state, I moved it to G1CollectorPolicy, and renamed it to
"should_update_surv_rate_group_predictors()" which is what it decides.

There is a bug in that method: the current code reads

  return _last_young_gc && !_in_marking_code;

which has been introduced in JDK-7097567. It should actually be:

  return _last_gc_was_young && !_in_marking_window;

I will fix that in JDK-8138752 to keep the cleanup separate from the bug
fix unless someone objects.

CR:
https://bugs.openjdk.java.net/browse/JDK-8138750
Webrev:
http://cr.openjdk.java.net/~tschatzl/8138750/webrev
Testing:
jprt

Thanks,
  Thomas