Unify symbols sharing across native scripts and runtime.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 841af8509aca8e92d637b8e9c5d9bc4b279d7ce1..552d4f5516e3feaeb6f2ff9b6e838e5e8c465c34 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -139,7 +139,7 @@ bool Object::IsPromise(Handle<Object> object) {
   auto isolate = js_object->GetIsolate();
   // TODO(dcarney): this should just be read from the symbol registry so as not
   // to be context dependent.
-  auto key = isolate->promise_status();
+  auto key = isolate->factory()->promise_status_symbol();
   // Shouldn't be possible to throw here.
   return JSObject::HasRealNamedProperty(js_object, key).FromJust();
 }