8235324: Dying objects are published from users of CollectedHeap::object_iterate

Reviewed-by: pliden, eosterlund, sjohanss, rkennke

src/hotspot/share/gc/shared/collectedHeap.hpp

@@ -387,6 +387,9 @@ class CollectedHeap : public CHeapObj<mtInternal> {
   // Iterate over all objects, calling "cl.do_object" on each.
   virtual void object_iterate(ObjectClosure* cl) = 0;
 
+  // Keep alive an object that was loaded with AS_NO_KEEPALIVE.
+  virtual void keep_alive(oop obj) {}
+
   // Returns the longest time (in ms) that has elapsed since the last
   // time that any part of the heap was examined by a garbage collection.
   virtual jlong millis_since_last_gc() = 0;