Configure stream wrapper for storing aggregates

im seeing some issues after running this patch with the advagg 2.3, so I'm going to work on this a little more and resubmit.

thanks, i will make that change and see if i can make it work.

Thanks to your input, i was able to implement the functionality i need via hook_advagg_save_aggregate_alter and hook_advagg_get_root_files_dir_alter. There is only one remaining component that i need to submit a patch for, which is to add the file extension to the temporary file name when saving aggregates in order to preserve the MIME type in the alternate stream wrapper. Patch is attached.

in case you are curious, here's what my implementation looks like:

/**
 * implements hook_advagg_save_aggregate_alter()
 */
function mymodule_advagg_save_aggregate_alter($files_to_save, $aggregate_settings, $other_parameters) {
  foreach ($files_to_save as $name => $file) {
    if (StringUtil::StartsWith($name, 'public')) {
      $new_name = preg_replace('/^public/', 's3', $name);
      ArrayUtil::ChangeKeyName($files_to_save, $name, $new_name);
    }
  }
}

/**
 * implements hook_advagg_get_root_files_dir_alter()
 */
function mymodule_advagg_get_root_files_dir_alter(&$css_paths, &$js_paths) {
  if ($css_paths[0] != 'public://advagg_css' || $js_paths[0] != 'public://advagg_js') {
    throw new Exception("unexpected value in the advagg css_paths or js_paths.");
  }
  $css_paths[0] = 's3://advagg_css';
  $js_paths[0] = 's3://advagg_js';
}

Thanks!