--- a/src/hotspot/share/memory/iterator.hpp	Fri Mar 15 18:59:21 2019 +0100
+++ b/src/hotspot/share/memory/iterator.hpp	Fri Mar 15 16:00:18 2019 -0400
@@ -36,6 +36,7 @@
 class KlassClosure;
 class ClassLoaderData;
 class Symbol;
+class Metadata;
 
 // The following classes are C++ `closures` for iterating over objects, roots and spaces
 
@@ -124,6 +125,11 @@
   virtual void do_cld(ClassLoaderData* cld) = 0;
 };
 
+class MetadataClosure : public Closure {
+ public:
+  virtual void do_metadata(Metadata* md) = 0;
+};
+
 
 class CLDToOopClosure : public CLDClosure {
   OopClosure*       _oop_closure;