first import

sites/all/modules/admin/includes/admin.theme.inc

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * Theme switcher admin block.
+ */
+function admin_block_theme() {
+  $themes = list_themes();
+  if (count($themes) > 2) {
+    return array(
+      'subject' => t('Switch theme'),
+      'content' => drupal_get_form('admin_block_theme_form', $themes),
+    );
+  }
+}
+
+/**
+ * Devel admin block form.
+ */
+function admin_block_theme_form($form, $form_state, $themes) {
+  $options = array();
+  foreach ($themes as $theme) {
+    if ($theme->status) {
+      $options[$theme->name] = isset($theme->info['name']) ? check_plain($theme->info['name']) : $theme->name;
+    }
+  }
+  $form = array();
+  $form['theme_default'] = array(
+    '#type' => 'radios',
+    '#options' => $options,
+    '#default_value' => variable_get('theme_default', 'garland'),
+  );
+  $form['submit'] = array(
+    '#type' => 'submit',
+    '#value' => t('Save configuration'),
+  );
+  $form['#submit'] = array('system_settings_form_submit');
+  return $form;
+}