[ic] Cache weak cells containing prototypes in respective PrototypeInfo objects.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index ad2f679f4d86e2ea5275f821e90a81a21c05bc3c..a4a7022ed8bbbc14b7988bb64b216fe7545b8ba3 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -12732,6 +12732,24 @@ Handle<Cell> Map::GetOrCreatePrototypeChainValidityCell(Handle<Map> map,
   return cell;
 }
 
+// static
+Handle<WeakCell> Map::GetOrCreatePrototypeWeakCell(Handle<JSObject> prototype,
+                                                   Isolate* isolate) {
+  DCHECK(!prototype.is_null());
+  Handle<PrototypeInfo> proto_info =
+      GetOrCreatePrototypeInfo(prototype, isolate);
+  Object* maybe_cell = proto_info->weak_cell();
+  // Return existing cell if it's already created.
+  if (maybe_cell->IsWeakCell()) {
+    Handle<WeakCell> cell(WeakCell::cast(maybe_cell), isolate);
+    DCHECK(!cell->cleared());
+    return cell;
+  }
+  // Otherwise create a new cell.
+  Handle<WeakCell> cell = isolate->factory()->NewWeakCell(prototype);
+  proto_info->set_weak_cell(*cell);
+  return cell;
+}
 
 // static
 void Map::SetPrototype(Handle<Map> map, Handle<Object> prototype,