[heap] Record references in the new code objects in heap::CopyCode.

src/heap/scavenger-inl.h

Index: src/heap/scavenger-inl.h
diff --git a/src/heap/scavenger-inl.h b/src/heap/scavenger-inl.h
index 0b6a0f48dfc2bb7c839b51cb571009ec225337b4..9671f3615fc29f45a4314ffd40ac145537f7745d 100644
--- a/src/heap/scavenger-inl.h
+++ b/src/heap/scavenger-inl.h
@@ -55,9 +55,9 @@ SlotCallbackResult Scavenger::CheckAndScavengeObject(Heap* heap,
     if (heap->InToSpace(object)) {
       return KEEP_SLOT;
     }
-  } else {
-    DCHECK(!heap->InNewSpace(object));
   }
+  // Slots can point to "to" space if the slot has been recorded multiple
+  // times in the remembered set. We remove the redundant slot now.
   return REMOVE_SLOT;
 }