Add Dictionary::RawFieldOfValueAt

For supporting use of dictionaries during GC, such as in the JS WeakRef
implementation.

Bug: v8:8179
Change-Id: Ide3f5c45d2602f13a1bcb1968b36f08881067090
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1972427Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65498}

src/objects/dictionary-inl.h

@@ -149,6 +149,12 @@ void Dictionary<Derived, Shape>::SetEntry(Isolate* isolate, InternalIndex entry,
   if (Shape::kHasDetails) DetailsAtPut(isolate, entry, details);
 }
 
+template <typename Derived, typename Shape>
+ObjectSlot Dictionary<Derived, Shape>::RawFieldOfValueAt(InternalIndex entry) {
+  return this->RawFieldOfElementAt(DerivedHashTable::EntryToIndex(entry) +
+                                   Derived::kEntryValueIndex);
+}
+
 template <typename Key>
 template <typename Dictionary>
 PropertyDetails BaseDictionaryShape<Key>::DetailsAt(Dictionary dict,

src/objects/dictionary.h

@@ -70,6 +70,9 @@ class EXPORT_TEMPLATE_DECLARE(V8_EXPORT_PRIVATE) Dictionary
   inline void SetEntry(Isolate* isolate, InternalIndex entry, Object key,
                        Object value, PropertyDetails details);
 
+  // Garbage collection support.
+  inline ObjectSlot RawFieldOfValueAt(InternalIndex entry);
+
   V8_WARN_UNUSED_RESULT static Handle<Derived> Add(
       Isolate* isolate, Handle<Derived> dictionary, Key key,
       Handle<Object> value, PropertyDetails details,