Ghost/ghost/admin/components/gh-role-selector.js

import GhostSelect from 'ghost/components/gh-select';

var RolesSelector = GhostSelect.extend({
    roles: Ember.computed.alias('options'),
    options: Ember.computed(function () {
        var rolesPromise = this.store.find('role', { permissions: 'assign' });

        return Ember.ArrayProxy.extend(Ember.PromiseProxyMixin)
            .create({promise: rolesPromise});
    })
});

export default RolesSelector;