RFR: Move heuristics from ShCollectorPolicy to ShHeap

[Roman Kennke]

Another refactoring in preparation of interleaving GC. It moves the
_heuristics out of ShCollectorPolicy and into ShHeap and (somewhat)
decouples heuristics from ShCollectorPolicy.

The reasoning behind this is that for interleaving minor/major GC I plan
to put a bunch of stuff into a 'context': control-thread, heuristics,
workers, cset, fset, and probably some more. Each context will work
somewhat independently on some part of the heap (e.g. young vs. old
gen). There will be one heuristic per context, but there will only be
one CollectorPolicy per GC. ShenandoahCollectorPolicy should eventually
become a pure implementation for CollectorPolicy and nothing else. Also
note that ShHeap is only a temporary home for the heuristics, they will
eventually go to the context class. The point of this patch is to
decouple heuristics from ShCollectorPolicy.

All the should* and can* methods are now called directly without hopping
through ShCollectorPolicy. However, all the record* methods remain in
the policy for now. I am not sure yet what to do with them: we may want
to call them per-context (e.g. a context recording only its own GC
activity) or globally (e.g. for stats) or both. I need to think this
through when I do the multi-context stuff.

http://cr.openjdk.java.net/~rkennke/heuristics-refactoring/webrev.00/

Passes hotspot_gc_shenandoah

Ok?

Roman