Code review comment for lp:~osomon/webbrowser-app/use-qml-SortFilterModel

> > Is there any particular reason why you prefer to declare this separately
> > instead as directly assigned to the topSitesModel.model ? Same applies
> > in other parts of the code. I don't mind but I would like to know if it
> > is just a style preference you have or if there are other reasons for it.
>
> Yes, there is a good reason for this structure. See comments 1 and 2 on bug
> #1495482.

Ok, let's leave it like this for now, but I am unconvinced by the fact that we can not use the two syntaxes interchangeably. I feel like there is some other bug related to roles in our custom models. Won't be the first time.
Anyway, this MR is good to go regardless of that.