ES6 symbols: extend V8 API to support symbols

src/handles.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 205 matching lines @@
                            Handle<Object> key,
                            Handle<Object> value,
                            PropertyAttributes attributes,
                            StrictModeFlag strict_mode);
 
 Handle<Object> ForceSetProperty(Handle<JSObject> object,
                                 Handle<Object> key,
                                 Handle<Object> value,
                                 PropertyAttributes attributes);
 
-Handle<Object> ForceDeleteProperty(Handle<JSObject> object,
-                                   Handle<Object> key);
+Handle<Object> DeleteProperty(Handle<JSObject> object, Handle<Object> key);
 
-Handle<Object> GetProperty(Handle<JSReceiver> obj,
-                           const char* name);
+Handle<Object> ForceDeleteProperty(Handle<JSObject> object, Handle<Object> key);
+
+Handle<Object> HasProperty(Handle<JSReceiver> obj, Handle<Object> key);
+
+Handle<Object> GetProperty(Handle<JSReceiver> obj, const char* name);
 
 Handle<Object> GetProperty(Isolate* isolate,
                            Handle<Object> obj,
                            Handle<Object> key);
 
 Handle<Object> SetPrototype(Handle<JSObject> obj, Handle<Object> value);
 
 Handle<Object> LookupSingleCharacterStringFromCode(Isolate* isolate,
                                                    uint32_t index);
 
@@ skipping 105 matching lines @@
   inline ~HandleDereferenceGuard();
  private:
   Isolate* isolate_;
   bool old_state_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HANDLES_H_