RFR(S) 8151633: Don't keep copies of the survivor lists and counts in the G1CollectorPolicy

[Mikael Gerdin]

Hi all,

G1CollectorPolicy contains copies of the linked list heads and tails 
present in YoungList.
In order to reduce the size of the G1CollectorPolicy, I suggest we 
remove them and have the policy access the ones in YoungList instead.

Webrev: http://cr.openjdk.java.net/~mgerdin/8151633/webrev.0/
Bug: https://bugs.openjdk.java.net/browse/JDK-8151633
Testing: JPRT (including runs with assertions that the pointers and 
lenght are in fact equal)

/Mikael