RFR(S): 8151808: Factor G1 heap sizing code out of the G1CollectorPolicy

[Mikael Gerdin]

Hi all,

The code responsible for determining the heap expansion amount is 
currently part of the class G1CollectorPolicy. The computations and data 
required by this functionality is completely independent of the other 
pieces of the class and could be moved to class of its own.

One could of course imagine that there could be situations where the 
sizing of the heap is influenced by the more general collector policy 
but there is nothing preventing that with the new model. The only 
difference would be that there would be a need for clearer API for such 
influences.

The patch is based on 8151711 and 8151637 but can be delivered 
separately, I just have them all in the same workspace.

Bug: https://bugs.openjdk.java.net/browse/JDK-8151808
Webrev: http://cr.openjdk.java.net/~mgerdin/8151808/webrev.0/
Testing: JPRT, RBT GC Testing
Perf testing in aggregate with some other policy changes shows no 
regressions or improvements.

/Mikael