**Description**

For a DAG that looks like this:

```
A >> B
```

If A fails, B goes into "upstream_failed" state. If a user then marks A "success", B will remain in "upstream_failed" state. It will not automatically start running. This scenario often happens if the failure of A is dealt with outside of Airflow and the user does not want Airflow to run A again. But he usually expect Airflow to run B after A is marked "success".

**Use case / motivation**

After A is marked "success", its downstream tasks B should be cleared automatically and get ready to be scheduled. To avoid changing this behaviour completely, there can be a toggle button next to "Success" that lets the user decide if he wants Airflow to automatically clear downstream tasks that are in "upstream_failed" state.
airflow/www/views.py
"""View to show Airflow Plugins"""
    default_view = 'list'
    class_permission_name = permissions.RESOURCE_PLUGIN
    method_permission_name = {
        'list': 'read',
    }
    base_permissions = [
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_ACCESS_MENU,
    ]
    plugins_attributes_to_dump = [
        "hooks",
        "executors",
        "macros",
        "admin_views",
        "flask_blueprints",
        "menu_links",
        "appbuilder_views",
        "appbuilder_menu_items",
        "global_operator_extra_links",
        "operator_extra_links",
        "source",
    ]
    @expose('/plugin')
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_PLUGIN),
        ]
    )
    def list(self):