ES6 symbols: extend V8 API to support symbols

src/runtime.h

Index: src/runtime.h
diff --git a/src/runtime.h b/src/runtime.h
index b16acd1d8e196fa62ab767acd2bfca9f380c212b..a3902b03303e20bdd3d9b1e9680bb094d55c0517 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -698,7 +698,13 @@ class Runtime : public AllStatic {
       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);