RFR [11]: 2018-11-04, Bulk backports to sh/jdk11

[Roman Kennke]

Ok. Thanks!

Roman


> http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20181104/webrev.01/
> 
> Recent improvements and bugfixes:
> 
>  [backport] Handle metadata induced GC
>  [backport] Adjust metaspace size during each GC
>  [backport] Remove fix-roots pass in ShHeap
>  [backport] Avoid write barrier during full GC
>  [backport] Pre-evac JVMTI roots + fixes
>  [backport] Protect risky conversion in ShenandoahHeap::millis_since_last_gc
>  [backport] Purge unnecessary time conversion in ShenandoahPhaseTimings::record_phase_time
>  [backport] Make heuristics tell if we can process references or unload classes
>  [backport] Factor out implicit/explicit GC requests
>  [backport] Concurrent cycle by default on any external GC request
>  [backport] Initial committed regions count can be more than max
> 
> Testing: tier3_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
>