Add missing Handle to GetOrCreatePrototypeChainValidityCell

Follow-up to 333219a7.

NOTRY=true
NOTREECHECKS=true

Review URL: https://codereview.chromium.org/1095503002

Cr-Commit-Position: refs/heads/master@{#27874}

src/objects.cc

@@ -10126,8 +10126,8 @@ Handle<Cell> Map::GetOrCreatePrototypeChainValidityCell(Handle<Map> map,
     PrototypeIterator iter(isolate, prototype);
     prototype = Handle<JSObject>::cast(PrototypeIterator::GetCurrent(iter));
   }
-  PrototypeInfo* proto_info =
-      PrototypeInfo::cast(prototype->map()->prototype_info());
+  Handle<PrototypeInfo> proto_info(
+      PrototypeInfo::cast(prototype->map()->prototype_info()));
   Object* maybe_cell = proto_info->validity_cell();
   // Return existing cell if it's still valid.
   if (maybe_cell->IsCell()) {