RFR (M): 8137082: Factor out G1 prediction code from G1CollectorPolicy and clean up

[Thomas Schatzl]

Hi all,

  can I have reviews for this cleanup change?

For dynamic IHOP (JDK-8136677) I intend to make the IHOP algorithm
mostly self-contained (and not just hack it into various places in
G1CollectorPolicy). For that I need the prediction algorithm to be more
self-contained to, so that the new code does not need to reference the
whole G1CollectorPolicy.

That is the reason for introducing the G1Predictions helper class that
contains all the necessary stuff to get a "prediction" from a sequence
of numbers without pulling in G1CollectorPolicy. Apart from that it
showed that by factoring out the prediction code there was some unused
code that could be deleted.

Since all methods in that new G1Predictions class were/are possible to
make const, I thought it would be a good idea to propagate that to the
predict_XXX() methods, and move their implementations to the cpp file
because they imo clutter up the interface a lot.

So, summing it up, there is no functionality change in this CR, just
some cleanup.

CR:
https://bugs.openjdk.java.net/browse/JDK-8137082
Webrev:
http://cr.openjdk.java.net/~tschatzl/8137082/webrev/
Testing:
jprt

Thanks,
  Thomas