Enable --verify-heap in release mode

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 479 matching lines @@
   CodeFlusher* code_flusher() { return code_flusher_; }
   inline bool is_code_flushing_enabled() const { return code_flusher_ != NULL; }
   void EnableCodeFlushing(bool enable);
 
   enum SweeperType {
     CONSERVATIVE,
     LAZY_CONSERVATIVE,
     PRECISE
   };
 
-#ifdef DEBUG
+#ifdef VERIFY_HEAP
   void VerifyMarkbitsAreClean();
   static void VerifyMarkbitsAreClean(PagedSpace* space);
   static void VerifyMarkbitsAreClean(NewSpace* space);
 #endif
 
   // Sweep a single page from the given space conservatively.
   // Return a number of reclaimed bytes.
   static intptr_t SweepConservatively(PagedSpace* space, Page* p);
 
   INLINE(static bool ShouldSkipEvacuationSlotRecording(Object** anchor)) {
@@ skipping 251 matching lines @@
 
   friend class Heap;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_