[Extensions] Don't allow gin::Define to be overridden

gin/converter.h

 // Copyright 2013 The Chromium 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 GIN_CONVERTER_H_
 #define GIN_CONVERTER_H_
 
 #include <string>
 #include <vector>
 
 #include "base/logging.h"
 #include "base/strings/string_piece.h"
 #include "gin/gin_export.h"
 #include "v8/include/v8.h"
 
 namespace gin {
 
 template<typename KeyType>
 bool SetProperty(v8::Isolate* isolate,
                  v8::Local<v8::Object> object,
                  KeyType key,
                  v8::Local<v8::Value> value) {
-  auto maybe = object->Set(isolate->GetCurrentContext(), key, value);
+  auto maybe =
+      object->DefineOwnProperty(isolate->GetCurrentContext(), key, value);
   return !maybe.IsNothing() && maybe.FromJust();
 }
 
 template<typename T>
 struct ToV8ReturnsMaybe {
   static const bool value = false;
 };
 
 template<typename T, typename Enable = void>
 struct Converter {};
@@ skipping 226 matching lines @@
 bool ConvertFromV8(v8::Isolate* isolate, v8::Local<v8::Value> input,
                    T* result) {
   return Converter<T>::FromV8(isolate, input, result);
 }
 
 GIN_EXPORT std::string V8ToString(v8::Local<v8::Value> value);
 
 }  // namespace gin
 
 #endif  // GIN_CONVERTER_H_