Revert "[heap] Make SlotSet allocation thread-safe and refactor code."

src/heap/spaces-inl.h

Index: src/heap/spaces-inl.h
diff --git a/src/heap/spaces-inl.h b/src/heap/spaces-inl.h
index 24c5f95a57b30f7afc4778699c92dbf99878e417..3ec2db51abde463061202c41d134f127dbc3c93d 100644
--- a/src/heap/spaces-inl.h
+++ b/src/heap/spaces-inl.h
@@ -330,16 +330,16 @@ void Page::MarkNeverAllocateForTesting() {
 
 void Page::MarkEvacuationCandidate() {
   DCHECK(!IsFlagSet(NEVER_EVACUATE));
-  DCHECK_NULL(slot_set<OLD_TO_OLD>());
-  DCHECK_NULL(typed_slot_set<OLD_TO_OLD>());
+  DCHECK_NULL(old_to_old_slots_);
+  DCHECK_NULL(typed_old_to_old_slots_);
   SetFlag(EVACUATION_CANDIDATE);
   reinterpret_cast<PagedSpace*>(owner())->free_list()->EvictFreeListItems(this);
 }
 
 void Page::ClearEvacuationCandidate() {
   if (!IsFlagSet(COMPACTION_WAS_ABORTED)) {
-    DCHECK_NULL(slot_set<OLD_TO_OLD>());
-    DCHECK_NULL(typed_slot_set<OLD_TO_OLD>());
+    DCHECK_NULL(old_to_old_slots_);
+    DCHECK_NULL(typed_old_to_old_slots_);
   }
   ClearFlag(EVACUATION_CANDIDATE);
   InitializeFreeListCategories();