Add zapping of Map contents in debug mode.

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4837 matching lines @@
   // |transitioned_map| when its elements_kind is changed to |elements_kind|.
   MUST_USE_RESULT MaybeObject* AddElementsTransition(
       ElementsKind elements_kind, Map* transitioned_map);
 
   // Returns the transitioned map for this map with the most generic
   // elements_kind that's found in |candidates|, or null handle if no match is
   // found at all.
   Handle<Map> FindTransitionedMap(MapHandleList* candidates);
   Map* FindTransitionedMap(MapList* candidates);
 
+  // Zaps the contents of backing data structures in debug mode. Note that the
+  // heap verifier (i.e. VerifyMarkingVisitor) relies on zapping of objects
+  // holding weak references when incremental marking is used.
+#ifdef DEBUG
+  void ZapInstanceDescriptors();
+  void ZapPrototypeTransitions();
+#endif
 
   // Dispatched behavior.
 #ifdef OBJECT_PRINT
   inline void MapPrint() {
     MapPrint(stdout);
   }
   void MapPrint(FILE* out);
 #endif
 #ifdef DEBUG
   void MapVerify();
@@ skipping 3792 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_