Para cuando se actualice el módulo, se debe modificar el archivo drupalchat.module para añadir la funcionalidad.

    $myuser = user_load($user->uid);
    foreach ($result as $buddy) {
        if($buddy->uid > 0) {
            $account = user_load($buddy->uid);
            /**
             * IF MANU
             * Compruebo si la classroom es igual
             */
            if ($myuser->field_classroom_simple_['und'][0]['target_id'] == $account->field_classroom_simple_['und'][0]['target_id']){
              $users[$buddy->uid] = array('name' => check_plain(format_username($account)), 'status' => $buddy->status);
              if(check_plain(variable_get('drupalchat_user_picture', 1)) == 1) {
                  $users[$buddy->uid]['p'] = drupalchat_return_pic_url_any_user(user_load($buddy->uid));
              }
            }
        }
        else {
          $users[$buddy->uid . '-' . $buddy->session] = array('name' => check_plain($buddy->name), 'status' => $buddy->status);
          if(check_plain(variable_get('drupalchat_user_picture', 1)) == 1) {
            $users[$buddy->uid . '-' . $buddy->session]['p'] = drupalchat_return_pic_url_any_user(user_load('0'));
          }
        }
    }