Update ObjectToString to Harmony-draft algorithm

include/v8.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.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 2112 matching lines @@
   // To minimize the potential for clashes, use qualified names as keys.
   static Local<Symbol> For(Isolate *isolate, Local<String> name);
 
   // Retrieve a global symbol. Similar to |For|, but using a separate
   // registry that is not accessible by (and cannot clash with) JavaScript code.
   static Local<Symbol> ForApi(Isolate *isolate, Local<String> name);
 
   // Well-known symbols
   static Local<Symbol> GetIterator(Isolate* isolate);
   static Local<Symbol> GetUnscopables(Isolate* isolate);
+  static Local<Symbol> GetToStringTag(Isolate* isolate);
 
   V8_INLINE static Symbol* Cast(v8::Value* obj);
 
  private:
   Symbol();
   static void CheckCast(v8::Value* obj);
 };
 
 
 /**
@@ skipping 4896 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_