**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
"""Customize permission names for FAB's builtin UserDBModelView."""
    _class_permission_name = permissions.RESOURCE_USER
    class_permission_name_mapping = {
        'resetmypassword': permissions.RESOURCE_MY_PASSWORD,
        'resetpasswords': permissions.RESOURCE_PASSWORD,
        'userinfoedit': permissions.RESOURCE_MY_PROFILE,
        'userinfo': permissions.RESOURCE_MY_PROFILE,
    }
    method_permission_name = {
        'add': 'create',
        'userinfo': 'read',
        'download': 'read',
        'show': 'read',
        'list': 'read',
        'edit': 'edit',
        'resetmypassword': 'read',
        'resetpasswords': 'read',
        'userinfoedit': 'edit',
        'delete': 'delete',
    }
    base_permissions = [
        permissions.ACTION_CAN_CREATE,
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_EDIT,
        permissions.ACTION_CAN_DELETE,
    ]
    @property
    def class_permission_name(self):