/**
  * Get URLs for icons if available.
  * @param MessageGroup $g
  * @param int $size Length of the edge of a bounding box to fit the icon.
  * @return null|array
  * @since 2013-04-01
  */
 public static function getIcon(MessageGroup $g, $size)
 {
     $icon = $g->getIcon();
     if (substr($icon, 0, 7) !== 'wiki://') {
         return null;
     }
     $formats = array();
     $filename = substr($icon, 7);
     $file = wfFindFile($filename);
     if (!$file) {
         wfWarn("Unknown message group icon file {$icon}");
         return null;
     }
     if ($file->isVectorized()) {
         $formats['vector'] = $file->getFullUrl();
     }
     $formats['raster'] = $file->createThumb($size, $size);
     return $formats;
 }