RFR: Adaptive thresholds for Traversal

[Aleksey Shipilev]

On 06/25/2018 11:53 AM, Roman Kennke wrote:
> This 'adopts' (i.e. mostly copy+pastes) the adaptive thresholds stuff
> from adaptive heuristics to be used in Traversal GC. Not sure if it
> should somehow be factored to be shared.
> 
> http://cr.openjdk.java.net/~rkennke/traversal-adaptive-thresholds/webrev.00/

Looks OK for now.

This assert is new:
  167   assert(!heap->has_forwarded_objects(), "no forwarded objects here");

...we used to return NONE when forwarded objects are in heap. I assume that never happens outside of
traversal cycle.

-Aleksey