new_contents: def DecoratorMixin(decorator):
      """
      Converts a decorator written for a function view into a mixin for a
      class-based view.
  
      ::
  
          LoginRequiredMixin = DecoratorMixin(login_required)
  
          class MyView(LoginRequiredMixin):
              pass
  
          class SomeView(DecoratorMixin(some_decorator),
                         DecoratorMixin(something_else)):
              pass
  
      """
  
      class Mixin(object):
          __doc__ = decorator.__doc__
  
          @classmethod
          def as_view(cls, *args, **kwargs):
              view = super(Mixin, cls).as_view(*args, **kwargs)
              return decorator(view)
  
      Mixin.__name__ = str('DecoratorMixin(%s)' % decorator.__name__)
      return Mixin
  
subject: Add mixin function.