ES6 symbols: extend V8 API to support symbols

src/runtime.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 680 matching lines @@
       PropertyAttributes attr,
       StrictModeFlag strict_mode);
 
   MUST_USE_RESULT static MaybeObject* ForceSetObjectProperty(
       Isolate* isolate,
       Handle<JSObject> object,
       Handle<Object> key,
       Handle<Object> value,
       PropertyAttributes attr);
 
-  MUST_USE_RESULT static MaybeObject* ForceDeleteObjectProperty(
+  MUST_USE_RESULT static MaybeObject* DeleteObjectProperty(
+      Isolate* isolate,
+      Handle<JSReceiver> object,
+      Handle<Object> key,
+      JSReceiver::DeleteMode mode);
+
+  MUST_USE_RESULT static MaybeObject* HasObjectProperty(
       Isolate* isolate,
       Handle<JSReceiver> object,
       Handle<Object> key);
 
   MUST_USE_RESULT static MaybeObject* GetObjectProperty(
       Isolate* isolate,
       Handle<Object> object,
       Handle<Object> key);
 
   // Helper functions used stubs.
@@ skipping 10 matching lines @@
 //---------------------------------------------------------------------------
 // Constants used by interface to runtime functions.
 
 class DeclareGlobalsEvalFlag:     public BitField<bool,         0, 1> {};
 class DeclareGlobalsNativeFlag:   public BitField<bool,         1, 1> {};
 class DeclareGlobalsLanguageMode: public BitField<LanguageMode, 2, 2> {};
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_