[api] Prototype WeakRef implementation

src/heap/objects-visiting.h

Index: src/heap/objects-visiting.h
diff --git a/src/heap/objects-visiting.h b/src/heap/objects-visiting.h
index abbb27a3267d7fba7618ccddf8930a93da667e50..3545072b6727ca589173bf6ab1c7c267ea297b85 100644
--- a/src/heap/objects-visiting.h
+++ b/src/heap/objects-visiting.h
@@ -60,6 +60,7 @@ class StaticVisitorBase : public AllStatic {
   V(SharedFunctionInfo)    \
   V(JSFunction)            \
   V(JSWeakCollection)      \
+  V(JSWeakRef)             \
   V(JSArrayBuffer)         \
   V(JSRegExp)
 
@@ -287,6 +288,7 @@ class StaticMarkingVisitor : public StaticVisitorBase {
   INLINE(static void VisitBytecodeArray(Map* map, HeapObject* object));
   INLINE(static void VisitSharedFunctionInfo(Map* map, HeapObject* object));
   INLINE(static void VisitWeakCollection(Map* map, HeapObject* object));
+  INLINE(static void VisitWeakRef(Map* map, HeapObject* object));
   INLINE(static void VisitJSFunction(Map* map, HeapObject* object));
   INLINE(static void VisitNativeContext(Map* map, HeapObject* object));