RFR: 8199925: Break out GC selection logic from GCArguments to GCSelector

[Kim Barrett]

> On Mar 21, 2018, at 9:11 AM, Per Liden <per.liden at oracle.com> wrote:
> 
> Hi,
> 
> Here's an updated webrev. I renamed GCSelector to GCConfig and it's now also the goto place for getting hold of the GCArguments instance for the currently selected GC.
> 
> http://cr.openjdk.java.net/~pliden/8199925/webrev.1
> 
> Btw, this is built on top of JDK-8199850 (Move parsing of VerifyGCType to G1) and JDK-8199918 (Shorten names of CollectedHeap::Name members), and the GCConfig::is_gc_* functions will eventually be used by JDK-8199927 (Make WhiteBox more GC agnostic).

I like this change, but don't have time right now to review it in detail, so don’t count me as a reviewer.

I do have a question though.  Why are there a bunch of private static members in GCConfig, rather
just some more file-scoped statics in gcConfig.cpp?