RFR [8]: Enable heap inspection for Shenandoah

[Aleksey Shipilev]

(facepalms)

This only affects sh/jdk8u, because we have this specific getter in 8. I think we have it disabled
before we implemented heap iteration, but never noticed during backports that 8 still has it
protected with the additional check. It was removed in 9 with:
  https://bugs.openjdk.java.net/browse/JDK-8077411

Fix:

diff -r 70ef3638af70 src/share/vm/gc_implementation/shenandoah/shenandoahHeap.hpp
--- a/src/share/vm/gc_implementation/shenandoah/shenandoahHeap.hpp      Mon Nov 19 10:47:38 2018 +0100
+++ b/src/share/vm/gc_implementation/shenandoah/shenandoahHeap.hpp      Tue Nov 27 13:05:20 2018 +0100
@@ -524,11 +524,11 @@
   bool card_mark_must_follow_store() const                    { return false;   }

   bool is_in_partial_collection(const void* p) shenandoah_not_implemented_return(false);
-  bool supports_heap_inspection() const { return false; }
+  bool supports_heap_inspection() const { return true; }

   void gc_prologue(bool b);


Testing: hotspot_tier3_gc_shenandoah, jmap -histo:live

Thanks,
-Aleksey