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 1f25a5d11b7dcd788a6541e41781eb98e826f6b7..a8c28f1cb29f90d7f6cc5a5724989aa1dfaf2892 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();
 }