WordPress at a glance
action is not described

wp_before_admin_bar_render action-hook . WP 3.1.0

Fires before the admin bar is rendered.

Usage

add_action( 'wp_before_admin_bar_render', 'action_function_name_7835' );
function action_function_name_7835(){
	// action...
}

Where the hook is called

wp_admin_bar_render()
wp-includes/admin-bar.php 90
do_action( 'wp_before_admin_bar_render' );

Where the hook is used (in WP core)

wp-includes/admin-bar.php 403
add_action( 'wp_before_admin_bar_render', 'wp_customize_support_script' );