RFR: 8191861: Move and refactor hSpaceCounters

[Stefan Karlsson]

Hi all,

Please review this patch to move and refactor HSpaceCounters.

http://cr.openjdk.java.net/~stefank/8191861/webrev.01
https://bugs.openjdk.java.net/browse/JDK-8191861

The patch moves hSpaceCounters.hpp/cpp out from gc/g1 into gc/shared, so 
that it can be reused by other GCs.

The patch also removes the dependency between HSpaceCounters and 
GenerationCounters. The passed in GenerationCounters object was only 
used to provide the name_space of the perf counter. This patch changes 
G1 to explicitly pass in the name_space string instead of the 
GenerationCounters.

This patch builds upon these two patches:
 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2017-November/029267.html
 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2017-November/029268.html

Thanks,
StefanK