MDL-41087 Backup: add progress tracking in slow steps

Adds calls to the new backup progress tracking API within various steps of the
backup system - previously it only tracked progress between steps, but some steps
can themselves be slow. This ensures the system displays progress (either by
moving the progress bar if possible, or by making the wibbler below it pulsate)
during nearly all of the backup process.

backup/util/structure/backup_structure_processor.class.php

@@ -37,9 +37,21 @@ class backup_structure_processor extends base_processor {
     protected $writer; // xml_writer where the processor is going to output data
     protected $vars;   // array of backup::VAR_XXX => helper value pairs to be used by source specifications
 
-    public function __construct(xml_writer $writer) {
+    /**
+     * @var core_backup_progress Progress tracker (null if none)
+     */
+    protected $progress;
+
+    /**
+     * Constructor.
+     *
+     * @param xml_writer $writer XML writer to save data
+     * @param core_backup_progress $progress Progress tracker (optional)
+     */
+    public function __construct(xml_writer $writer, core_backup_progress $progress = null) {
         $this->writer = $writer;
-        $this->vars   = array();
+        $this->progress = $progress;
+        $this->vars = array();
     }
 
     public function set_var($key, $value) {
@@ -83,6 +95,9 @@ class backup_structure_processor extends base_processor {
     public function post_process_nested_element(base_nested_element $nested) {
         // Send close tag to xml_writer
         $this->writer->end_tag($nested->get_name());
+        if ($this->progress) {
+            $this->progress->progress();
+        }
     }
 
     public function process_final_element(base_final_element $final) {
@@ -93,6 +108,9 @@ class backup_structure_processor extends base_processor {
                 $attrarr[$attribute->get_name()] = $attribute->get_value();
             }
             $this->writer->full_tag($final->get_name(), $final->get_value(), $attrarr);
+            if ($this->progress) {
+                $this->progress->progress();
+            }
             // Annotate current value if configured to do so
             $final->annotate($this->get_var(backup::VAR_BACKUPID));
         }