[proxies] allow duplicate keys for [[OwnPropertyKeys]] trap.

src/json-stringifier.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_JSON_STRINGIFIER_H_
 #define V8_JSON_STRINGIFIER_H_
 
 #include "src/conversions.h"
 #include "src/lookup.h"
 #include "src/messages.h"
@@ skipping 549 matching lines @@
             EXCEPTION);
       }
       Result result = SerializeProperty(property, comma, key);
       if (!comma && result == SUCCESS) comma = true;
       if (result == EXCEPTION) return result;
     }
   } else {
     Handle<FixedArray> contents;
     ASSIGN_RETURN_ON_EXCEPTION_VALUE(
         isolate_, contents,
-        JSReceiver::GetKeys(object, JSReceiver::OWN_ONLY, ENUMERABLE_STRINGS),
-        EXCEPTION);
+        JSReceiver::GetKeys(object, OWN_ONLY, ENUMERABLE_STRINGS), EXCEPTION);
 
     for (int i = 0; i < contents->length(); i++) {
       Object* key = contents->get(i);
       Handle<String> key_handle;
       MaybeHandle<Object> maybe_property;
       if (key->IsString()) {
         key_handle = Handle<String>(String::cast(key), isolate_);
         maybe_property = Object::GetPropertyOrElement(object, key_handle);
       } else {
         DCHECK(key->IsNumber());
@@ skipping 97 matching lines @@
     } else {
       SerializeString_<uc16, uc16>(object);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_JSON_STRINGIFIER_H_