RFR: 8199027: Make protected members private in G1Policy

[Erik Helin]

Hi all,

this tiny patch removes the (unnecessary) use of `protected` visibility 
from the class G1Policy, the members that were protected can just be 
private.

Issue:
https://bugs.openjdk.java.net/browse/JDK-8199027

Patch:
http://cr.openjdk.java.net/~ehelin/8199027/00/

Testing:
- make run-test-tier1

Thanks,
Erik