[es6] Partially implement Reflect.getOwnPropertyDescriptor.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index dc503e96ed5e69705492fa097f533da5d6025515..cd5b15ceb076b91b8d4c04e0ab8951c84d6aa2df 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1893,7 +1893,7 @@ class JSReceiver: public HeapObject {
                                         ShouldThrow should_throw);
 
   static bool GetOwnPropertyDescriptor(Isolate* isolate,
-                                       Handle<JSObject> object,
+                                       Handle<JSReceiver> object,
                                        Handle<Object> key,
                                        PropertyDescriptor* desc);
   static bool GetOwnPropertyDescriptor(LookupIterator* it,