Eliminate invalid pointers in store buffer after marking.

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 3b0815e8295dca8dd02b8e0c1b3ad41527f4bdf3..fbe8bb953b680075fd1e13af5fcc65ceffcdd21d 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -670,6 +670,14 @@ class MarkCompactCollector {
 
   void OverApproximateWeakClosure();
 
+  // The following four methods can just be called after marking, when the
+  // whole transitive closure is known. They must be called before sweeping
+  // when mark bits are still intact.
+  bool IsSlotInBlackObject(Page* p, Address slot);
+  bool IsSlotInBlackObjectSlow(Page* p, Address slot);
+  bool IsSlotInLiveObject(HeapObject** address, HeapObject* object);
+  void VerifyIsSlotInLiveObject(HeapObject** address, HeapObject* object);
+
  private:
   class SweeperTask;