--- a/src/hotspot/share/gc/shared/collectedHeap.hpp	Thu Nov 08 18:10:15 2018 -0300
+++ b/src/hotspot/share/gc/shared/collectedHeap.hpp	Thu Nov 08 23:31:08 2018 +0100
@@ -580,6 +580,11 @@
 
   virtual size_t obj_size(oop obj) const;
 
+  // Cells are memory slices allocated by the allocator. Objects are initialized
+  // in cells. The cell itself may have a header, found at a negative offset of
+  // oops. Usually, the size of the cell header is 0, but it may be larger.
+  virtual ptrdiff_t cell_header_size() const { return 0; }
+
   // Non product verification and debugging.
 #ifndef PRODUCT
   // Support for PromotionFailureALot.  Return true if it's time to cause a