[runtime] Add MapUpdater class that manages all kinds of map updates.

src/property.h

 // Copyright 2014 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_PROPERTY_H_
 #define V8_PROPERTY_H_
 
 #include <iosfwd>
 
 #include "src/factory.h"
@@ skipping 67 matching lines @@
              Representation representation, int field_index = 0)
       : key_(key),
         value_(value),
         details_(attributes, type, representation, field_index) {
     DCHECK(key->IsUniqueName());
     DCHECK_IMPLIES(key->IsPrivate(), !details_.IsEnumerable());
   }
 
   friend class DescriptorArray;
   friend class Map;
+  friend class MapUpdater;
 };
 
 std::ostream& operator<<(std::ostream& os, const Descriptor& d);
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PROPERTY_H_