Enable --verify-heap in release mode

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 14f81f89a93534a9c33652ca2f8ae6d7d9b45928..82ade6f011d4dd3514b9aa7b0cc2a21870da44bc 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -5096,14 +5096,14 @@ class Map: public HeapObject {
   Handle<Map> FindTransitionedMap(MapHandleList* candidates);
   Map* FindTransitionedMap(MapList* candidates);
 
-  // Zaps the contents of backing data structures in debug mode. Note that the
+  // Zaps the contents of backing data structures. Note that the
   // heap verifier (i.e. VerifyMarkingVisitor) relies on zapping of objects
   // holding weak references when incremental marking is used, because it also
   // iterates over objects that are otherwise unreachable.
-#ifdef DEBUG
+  // In general we only want to call these functions in release mode when
+  // heap verification is turned on.
   void ZapPrototypeTransitions();
   void ZapTransitions();
-#endif
 
   // Dispatched behavior.
 #ifdef OBJECT_PRINT