Replace slots buffer with remembered set.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index f7283fa1ce2810a752abfd5ec56dbdffa9f21aef..88310422b4eba65f168d9065895ed4fe0302912e 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -5574,6 +5574,7 @@ void Heap::ClearRecordedSlot(HeapObject* object, Object** slot) {
     Page* page = Page::FromAddress(slot_addr);
     DCHECK_EQ(page->owner()->identity(), OLD_SPACE);
     RememberedSet<OLD_TO_NEW>::Remove(page, slot_addr);
+    RememberedSet<OLD_TO_OLD>::Remove(page, slot_addr);
   }
 }
 
@@ -5586,6 +5587,7 @@ void Heap::ClearRecordedSlotRange(HeapObject* object, Object** start,
     Page* page = Page::FromAddress(start_addr);
     DCHECK_EQ(page->owner()->identity(), OLD_SPACE);
     RememberedSet<OLD_TO_NEW>::RemoveRange(page, start_addr, end_addr);
+    RememberedSet<OLD_TO_OLD>::RemoveRange(page, start_addr, end_addr);
   }
 }