Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

1. Create a view with a detail_route with a schema kwarg

        class AViewSet(GenericViewSet):
            @detail_route(schema=AutoSchema(manual_fields=[
                coreapi.Field(
                    "my_extra_field",
                    required=True,
                    location="path",
                    schema=coreschema.String()
                ),
            ]))
            def a_detail_route(self, request, my_normal_field):
                pass

2. Register the view with a router

        router = routers.SimpleRouter()
        router.register(r'detail', AViewSet, base_name='detail')
        routes = router.urls

3. Attempt to generate a schema from the view

        callback = routes[0].callback
        generator = SchemaGenerator()
        view = generator.create_view(callback, 'GET')
        link = view.schema.get_link('/a/url/{id}/', 'GET', '')

Expected behavior

A schema is generated for the detail route using the given AutoSchema.

Actual behavior

Crashes:
AttributeError: 'AutoSchema' object has no attribute '_view'