[compiler] MakeRefAssumeMemoryFence in MapRef::FindFieldOwner

The current map is safe to read, and backpointers (read inside
Map::FindFieldOwner) are immutable after initialization.

Bug: v8:7790
Change-Id: I10329a44b8fa1e831fc2b52c0bc16c81891af784
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3068949
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76058}

src/compiler/heap-refs.cc

@@ -2170,8 +2170,9 @@ MapRef MapRef::FindFieldOwner(InternalIndex descriptor_index) const {
   // TODO(solanes, v8:7790): Consider caching the result of the field owner on
   // the descriptor array. It would be useful for same map as well as any
   // other map sharing that descriptor array.
-  return MapRef(broker(), broker()->GetOrCreateData(object()->FindFieldOwner(
-                              broker()->isolate(), descriptor_index)));
+  return MakeRefAssumeMemoryFence(
+      broker(),
+      object()->FindFieldOwner(broker()->isolate(), descriptor_index));
 }
 
 ObjectRef MapRef::GetFieldType(InternalIndex descriptor_index) const {