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..9b19a0862d384246fe649971dd695a8e8e20421b 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1289,14 +1289,9 @@ 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();
+bool Object::IsErrorObject(Handle<Object> object) {

[Toon Verwaest, 2016/06/23 17:09:30]

This doesn't need to be a static method anymore. You can just do IsHeapObject()
&& HeapObject::cast(this)->IsJSError() ... :)

+  return object->IsHeapObject() &&
+         Handle<HeapObject>::cast(object)->IsJSError();
 }