Get the target field index when transitioning.

src/json-parser.h

 // Copyright 2011 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 271 matching lines @@
       return ParseJsonArray();
     default:
       return ReportUnexpectedCharacter();
   }
 }
 
 
 // Parse a JSON object. Position must be right at '{'.
 template <bool seq_ascii>
 Handle<Object> JsonParser<seq_ascii>::ParseJsonObject() {
-  int current_index = 0;
   Handle<Object> prototype;
   Handle<JSFunction> object_constructor(
       isolate()->native_context()->object_function());
   Handle<JSObject> json_object =
       isolate()->factory()->NewJSObject(object_constructor);
   ASSERT_EQ(c0_, '{');
 
   AdvanceSkipWhitespace();
   if (c0_ != '}') {
     do {
@@ skipping 29 matching lines @@
         if (key.is_null() || c0_ != ':') return ReportUnexpectedCharacter();
 
         AdvanceSkipWhitespace();
         Handle<Object> value = ParseJsonValue();
         if (value.is_null()) return ReportUnexpectedCharacter();
 
         if (key->Equals(isolate()->heap()->Proto_symbol())) {
           prototype = value;
         } else {
           if (JSObject::TryTransitionToField(json_object, key)) {
-            json_object->FastPropertyAtPut(current_index++, *value);
+            int index = json_object->LastAddedFieldIndex();
+            json_object->FastPropertyAtPut(index, *value);
           } else {
             JSObject::SetLocalPropertyIgnoreAttributes(
                 json_object, key, value, NONE);
-            current_index = json_object->NumberOfLocalProperties();
           }
         }
       }
     } while (MatchSkipWhiteSpace(','));
     if (c0_ != '}') {
       return ReportUnexpectedCharacter();
     }
     if (!prototype.is_null()) SetPrototype(json_object, prototype);
   }
   AdvanceSkipWhitespace();
@@ skipping 322 matching lines @@
   }
   ASSERT_EQ('"', c0_);
   // Advance past the last '"'.
   AdvanceSkipWhitespace();
   return result;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_PARSER_H_