ES6 symbols: extend V8 API to support symbols

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index c69713e44e8e4422bcfc19f41fe3f58c6f8d208d..245b1c3f1479dab793ff341b1859e4f10224ebd2 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -223,11 +223,13 @@ Handle<Object> ForceSetProperty(Handle<JSObject> object,
                                 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,