[offthread] Don't set marking bit on off-thread large pages

Bug: chromium:1088350
Change-Id: I9dc9f6b323ebe2e751167880acad0eed3584222a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2224227
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68094}

src/heap/large-spaces.cc

@@ -224,7 +224,8 @@ void LargeObjectSpace::AddPage(LargePage* page, size_t object_size) {
   page_count_++;
   memory_chunk_list_.PushBack(page);
   page->set_owner(this);
-  page->SetOldGenerationPageFlags(heap()->incremental_marking()->IsMarking());
+  page->SetOldGenerationPageFlags(!is_off_thread() &&
+                                  heap()->incremental_marking()->IsMarking());
 }
 
 void LargeObjectSpace::RemovePage(LargePage* page, size_t object_size) {