Eliminate invalid pointers in store buffer after marking.

src/heap/store-buffer.h

Index: src/heap/store-buffer.h
diff --git a/src/heap/store-buffer.h b/src/heap/store-buffer.h
index 30ef18f54f08f9c924f206dfde212e6c55c77e1f..f353b1df2c95d9258fbe230f26ba647c1f1100c1 100644
--- a/src/heap/store-buffer.h
+++ b/src/heap/store-buffer.h
@@ -105,6 +105,13 @@ class StoreBuffer {
 
   void Filter(int flag);
 
+  // Eliminates all stale store buffer entries from the store buffer, i.e.,
+  // slots that are not part of live objects anymore. This method must be
+  // called after marking, when the whole transitive closure is known and
+  // must be called before sweeping when mark bits are still intact.
+  void ClearInvalidStoreBufferEntries();
+  void VerifyValidStoreBufferEntries();
+
  private:
   Heap* heap_;