Remove prototype key from the prototype transitions since its also embedded in the target map.

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 5965 matching lines @@
   inline Object* GetBackPointer();
   inline void SetBackPointer(Object* value,
                              WriteBarrierMode mode = UPDATE_WRITE_BARRIER);
   inline void init_back_pointer(Object* undefined);
 
   // [prototype transitions]: cache of prototype transitions.
   // Prototype transition is a transition that happens
   // when we change object's prototype to a new one.
   // Cache format:
   //    0: finger - index of the first free cell in the cache
-  //    1: back pointer that overlaps with prototype transitions field.
-  //    2 + 2 * i: prototype
-  //    3 + 2 * i: target map
+  //    1 + i: target map
   inline FixedArray* GetPrototypeTransitions();
   inline bool HasPrototypeTransitions();
 
+  static const int kProtoTransitionNumberOfEntriesOffset = 0;
   static const int kProtoTransitionHeaderSize = 1;
-  static const int kProtoTransitionNumberOfEntriesOffset = 0;
-  static const int kProtoTransitionElementsPerEntry = 2;
-  static const int kProtoTransitionPrototypeOffset = 0;
-  static const int kProtoTransitionMapOffset = 1;
 
   inline int NumberOfProtoTransitions() {
     FixedArray* cache = GetPrototypeTransitions();
     if (cache->length() == 0) return 0;
     return
         Smi::cast(cache->get(kProtoTransitionNumberOfEntriesOffset))->value();
   }
 
   inline void SetNumberOfProtoTransitions(int value) {
     FixedArray* cache = GetPrototypeTransitions();
@@ skipping 4976 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_