RFR: Code cache roots styles

[Aleksey Shipilev]

Hi,

I'd like to continue doing experiments with code cache support. There good
improvements to be reaped with oop and cset filtering. To get better testing I
suggest we push the refactoring and selector for code cache root styles, and
continue:
  http://cr.openjdk.java.net/~shade/shenandoah/codecache-styles/webrev.01/

Testing: hotspot_gc_shenandoah, jcstress

Thanks,
-Aleksey