Use instance type in Object::IsErrorObject().

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index aa4c3349fa5eedf931a0322efc4be662045cd49e..1faeec619f710e1b5c7837324bc47ed8b9ae5504 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1291,12 +1291,8 @@ Maybe<bool> Object::SetPropertyWithDefinedSetter(Handle<Object> receiver,
 // static
 bool Object::IsErrorObject(Isolate* isolate, Handle<Object> object) {

[Toon Verwaest, 2016/06/23 14:22:40]

This doesn't need the isolate anymore.

What about doing:
Object::IsErrorObject() {
  return IsHeapObject() && HeapObject::cast(this)->IsErrorObject()
}
HeapObject::IsErrorObject() {
  return map()->instance_type() == JS_ERROR_TYPE;
}

and just calling IsErrorObject in api.cc?

   if (!object->IsJSObject()) return false;
-  // Use stack_trace_symbol as proxy for [[ErrorData]].
-  Handle<Name> symbol = isolate->factory()->stack_trace_symbol();
-  Maybe<bool> has_stack_trace =
-      JSReceiver::HasOwnProperty(Handle<JSReceiver>::cast(object), symbol);
-  DCHECK(!has_stack_trace.IsNothing());
-  return has_stack_trace.FromJust();
+  Handle<JSObject> js_object = Handle<JSObject>::cast(object);
+  return js_object->map()->instance_type() == JS_ERROR_TYPE;
 }