Make Error.prototype.toString spec compliant; and fix various side-effect-free error printing metho…

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 3e5bd4300e121fd9ffa35886a9ce4a60eb46c4b0..279ed1dbaaaa44297afcba33d4cb35e1d7707342 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1163,6 +1163,18 @@ 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();
+}
+
+
+// static
 bool JSObject::AllCanRead(LookupIterator* it) {
   // Skip current iteration, it's in state ACCESS_CHECK or INTERCEPTOR, both of
   // which have already been checked.