plugin add action hook is not working :

Nothing is wrong with your code. Just change the $Wp_Admin_Bar to all lowercase

   function wp_add_google_link(){
global $wp_admin_bar;
var_dump($wp_admin_bar);
$wp_admin_bar->add_menu(array(
    'id'=>'google_analytics',
    'title'=>'GoogleAnalytics',
    'href'=>'https://google.com/analytics'
    ));
}

add_action('admin_bar_menu','wp_add_google_link');