Use instance type in Object::IsErrorObject().

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index e52c8c05b0af947ffd5e7bca25e3445f4d6babf8..a91ea0499c94dd352a88d800ff991200e21c14c9 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) {
   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<JSReceiver> receiver = Handle<JSReceiver>::cast(object);

[Toon Verwaest, 2016/06/23 12:04:39]

since you know it's a JSObject, you might as well cast to that :)

[Franzi, 2016/06/23 14:10:19]

Done.

+  return receiver->map()->instance_type() == JS_ERROR_TYPE;
 }