[api] Prototype WeakRef implementation

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 5075f6162be2c5e31322d51fb1609576bb23a8ce..e127ec1cd8208c229825d5b3d09acb1c03d55323 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -199,6 +199,7 @@ using v8::MemoryPressureLevel;
   V(UnseededNumberDictionary, code_stubs, CodeStubs)                           \
   V(FixedArray, materialized_objects, MaterializedObjects)                     \
   V(FixedArray, microtask_queue, MicrotaskQueue)                               \
+  V(FixedArray, weak_refs, WeakRefs)                                           \
   V(FixedArray, detached_contexts, DetachedContexts)                           \
   V(ArrayList, retained_maps, RetainedMaps)                                    \
   V(WeakHashTable, weak_object_to_code_table, WeakObjectToCodeTable)           \