Allow users of the V8 API to distinguish between unset and undefined HiddenValues

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 1978 matching lines @@
   // of its prototype, and if it's a detached proxy, then you can't have
   // hidden properties.
 
   // Sets a hidden property on this object. Returns this object if successful,
   // undefined if called on a detached proxy.
   static Handle<Object> SetHiddenProperty(Handle<JSObject> obj,
                                           Handle<Name> key,
                                           Handle<Object> value);
   // Returns a failure if a GC is required.
   MUST_USE_RESULT MaybeObject* SetHiddenProperty(Name* key, Object* value);
-  // Gets the value of a hidden property with the given key. Returns undefined
+  // Gets the value of a hidden property with the given key. Returns the hole
   // if the property doesn't exist (or if called on a detached proxy),
   // otherwise returns the value set for the key.
   Object* GetHiddenProperty(Name* key);
   // Deletes a hidden property. Deleting a non-existing property is
   // considered successful.
   void DeleteHiddenProperty(Name* key);
   // Returns true if the object has a property with the hidden string as name.
   bool HasHiddenProperties();
 
   static int GetIdentityHash(Handle<JSObject> obj);
@@ skipping 7715 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_