Implement explicit back pointers in transition tree.

src/mark-compact.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 624 matching lines @@
   INLINE(void MarkObject(HeapObject* obj, MarkBit mark_bit));
 
   INLINE(bool MarkObjectWithoutPush(HeapObject* object));
   INLINE(void MarkObjectAndPush(HeapObject* value));
 
   // Marks the object black.  This is for non-incremental marking.
   INLINE(void SetMark(HeapObject* obj, MarkBit mark_bit));
 
   void ProcessNewlyMarkedObject(HeapObject* obj);
 
-  // Creates back pointers for all map transitions, stores them in
-  // the prototype field.  The original prototype pointers are restored
-  // in ClearNonLiveTransitions().  All JSObject maps
-  // connected by map transitions have the same prototype object, which
-  // is why we can use this field temporarily for back pointers.
-  void CreateBackPointers();
-
   // Mark a Map and its DescriptorArray together, skipping transitions.
   void MarkMapContents(Map* map);
   void MarkAccessorPairSlot(HeapObject* accessors, int offset);
   void MarkDescriptorArray(DescriptorArray* descriptors);
 
   // Mark the heap roots and all objects reachable from them.
   void MarkRoots(RootMarkingVisitor* visitor);
 
   // Mark the symbol table specially.  References to symbols from the
   // symbol table are weak.
@@ skipping 100 matching lines @@
 
   friend class Heap;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_