MDL-28505 Backup: Asynchronous backup and restore

This patch adds asynchronous backup and restore functionality
to Moodle. This is an optional feature and is not enabled by
default. It can be enabled by site administrators.
Asynchronous backup and restores are actioned by the Moodle
adhoc task API. The progress of backup and restores is
displayedin the Moodle UI.  Users can also be sent a message
when a backup or restore operation completes via the
Moodle messaging API.

backup/util/dbops/backup_controller_dbops.class.php

@@ -641,4 +641,31 @@ abstract class backup_controller_dbops extends backup_dbops {
             }
         }
     }
+
+    /**
+     * Get the progress details of a backup operation.
+     * Get backup records directly from database, if the backup has successfully completed
+     * there will be no controller object to load.
+     *
+     * @param string $backupid The backup id to query.
+     * @return array $progress The backup progress details.
+     */
+    public static function get_progress($backupid) {
+        global $DB;
+
+        $progress = array();
+        $backuprecord = $DB->get_record(
+            'backup_controllers',
+            array('backupid' => $backupid),
+            'status, progress, operation',
+            MUST_EXIST);
+
+        $status = $backuprecord->status;
+        $progress = $backuprecord->progress;
+        $operation = $backuprecord->operation;
+
+        $progress = array('status' => $status, 'progress' => $progress, 'backupid' => $backupid, 'operation' => $operation);
+
+        return $progress;
+    }
 }