Fix DCHECK in Map::TryUpdateSlow

R=jarin@chromium.org

Bug: chromium:940423
Change-Id: I9e357d8fe424b291bc25a1d389696df88deda6a3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1514735Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60160}

src/objects/map.cc

@@ -1029,8 +1029,10 @@ Map Map::TryUpdateSlow(Isolate* isolate, Map old_map) {
                  .SearchSpecial(info.integrity_level_symbol);
   }
 
-  DCHECK_EQ(old_map->elements_kind(), result->elements_kind());
-  DCHECK_EQ(old_map->instance_type(), result->instance_type());
+  DCHECK_IMPLIES(!result.is_null(),
+                 old_map->elements_kind() == result->elements_kind());
+  DCHECK_IMPLIES(!result.is_null(),
+                 old_map->instance_type() == result->instance_type());
   return result;
 }