Access old space marking bits from runtime only when incremental marking is in MARKING state.

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 92 matching lines @@
 
   INLINE(static void BlackToGrey(HeapObject* obj)) {
     BlackToGrey(MarkBitFrom(obj));
   }
 
   INLINE(static void AnyToGrey(MarkBit markbit)) {
     markbit.Set();
     markbit.Next().Set();
   }
 
-  // Returns true if the the object whose mark is transferred is marked black.
-  bool TransferMark(Address old_start, Address new_start);
+  void TransferMark(Address old_start, Address new_start);
 
 #ifdef DEBUG
   enum ObjectColor {
     BLACK_OBJECT,
     WHITE_OBJECT,
     GREY_OBJECT,
     IMPOSSIBLE_COLOR
   };
 
   static const char* ColorName(ObjectColor color) {
@@ skipping 911 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_