Revert part of 11727 as it sometimes tanked V8 benchmark (raytrace) performance

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 4731 matching lines @@
   inline void set_attached_to_shared_function_info(bool value);
 
   inline bool attached_to_shared_function_info();
 
   // Tells whether the map is shared between objects that may have different
   // behavior. If true, the map should never be modified, instead a clone
   // should be created and modified.
   inline void set_is_shared(bool value);
   inline bool is_shared();
 
-  // Tells whether the map is used for an object that is a prototype for another
-  // object or is the prototype on a function.  Such maps are made faster by
-  // tweaking the heuristics that distinguish between regular object-oriented
-  // objects and the objects that are being used as hash maps.  This flag is
-  // for optimization, not correctness.
-  inline void set_used_for_prototype(bool value);
-  inline bool used_for_prototype();
-
   // Tells whether the instance needs security checks when accessing its
   // properties.
   inline void set_is_access_check_needed(bool access_check_needed);
   inline bool is_access_check_needed();
 
   // [prototype]: implicit prototype object.
   DECL_ACCESSORS(prototype, Object)
 
   // [constructor]: points back to the function responsible for this map.
   DECL_ACCESSORS(constructor, Object)
@@ skipping 167 matching lines @@
   typedef void (*TraverseCallback)(Map* map, void* data);
 
   void TraverseTransitionTree(TraverseCallback callback, void* data);
 
   // When you set the prototype of an object using the __proto__ accessor you
   // need a new map for the object (the prototype is stored in the map).  In
   // order not to multiply maps unnecessarily we store these as transitions in
   // the original map.  That way we can transition to the same map if the same
   // prototype is set, rather than creating a new map every time.  The
   // transitions are in the form of a map where the keys are prototype objects
-  // and the values are the maps the are transitioned to.  The special key
-  // the_hole denotes the map we should transition to when the
-  // used_for_prototype flag is set.
+  // and the values are the maps the are transitioned to.
   static const int kMaxCachedPrototypeTransitions = 256;
 
   Map* GetPrototypeTransition(Object* prototype);
 
   MUST_USE_RESULT MaybeObject* PutPrototypeTransition(Object* prototype,
                                                       Map* map);
 
   static const int kMaxPreAllocatedPropertyFields = 255;
 
   // Layout description.
@@ skipping 75 matching lines @@
   static const int8_t kMaximumBitField2FastHoleyElementValue =
       static_cast<int8_t>((FAST_HOLEY_ELEMENTS + 1) <<
                           Map::kElementsKindShift) - 1;
   static const int8_t kMaximumBitField2FastHoleySmiElementValue =
       static_cast<int8_t>((FAST_HOLEY_SMI_ELEMENTS + 1) <<
                           Map::kElementsKindShift) - 1;
 
   // Bit positions for bit field 3
   static const int kIsShared = 0;
   static const int kFunctionWithPrototype = 1;
-  static const int kUsedForPrototype = 2;
 
   typedef FixedBodyDescriptor<kPointerFieldsBeginOffset,
                               kPointerFieldsEndOffset,
                               kSize> BodyDescriptor;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Map);
 };
 
 
@@ skipping 3736 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_