diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-admin/includes/class-bulk-upgrader-skin.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-admin/includes/class-bulk-upgrader-skin.php	Mon Oct 14 17:39:30 2019 +0200
@@ -0,0 +1,175 @@
+<?php
+/**
+ * Upgrader API: Bulk_Upgrader_Skin class
+ *
+ * @package WordPress
+ * @subpackage Upgrader
+ * @since 4.6.0
+ */
+
+/**
+ * Generic Bulk Upgrader Skin for WordPress Upgrades.
+ *
+ * @since 3.0.0
+ * @since 4.6.0 Moved to its own file from wp-admin/includes/class-wp-upgrader-skins.php.
+ *
+ * @see WP_Upgrader_Skin
+ */
+class Bulk_Upgrader_Skin extends WP_Upgrader_Skin {
+	public $in_loop = false;
+	/**
+	 * @var string|false
+	 */
+	public $error = false;
+
+	/**
+	 *
+	 * @param array $args
+	 */
+	public function __construct($args = array()) {
+		$defaults = array( 'url' => '', 'nonce' => '' );
+		$args = wp_parse_args($args, $defaults);
+
+		parent::__construct($args);
+	}
+
+	/**
+	 */
+	public function add_strings() {
+		$this->upgrader->strings['skin_upgrade_start'] = __('The update process is starting. This process may take a while on some hosts, so please be patient.');
+		/* translators: 1: Title of an update, 2: Error message */
+		$this->upgrader->strings['skin_update_failed_error'] = __('An error occurred while updating %1$s: %2$s');
+		/* translators: 1: Title of an update */
+		$this->upgrader->strings['skin_update_failed'] = __('The update of %1$s failed.');
+		/* translators: 1: Title of an update */
+		$this->upgrader->strings['skin_update_successful'] = __( '%1$s updated successfully.' );
+		$this->upgrader->strings['skin_upgrade_end'] = __('All updates have been completed.');
+	}
+
+	/**
+	 *
+	 * @param string $string
+	 */
+	public function feedback($string) {
+		if ( isset( $this->upgrader->strings[$string] ) )
+			$string = $this->upgrader->strings[$string];
+
+		if ( strpos($string, '%') !== false ) {
+			$args = func_get_args();
+			$args = array_splice($args, 1);
+			if ( $args ) {
+				$args = array_map( 'strip_tags', $args );
+				$args = array_map( 'esc_html', $args );
+				$string = vsprintf($string, $args);
+			}
+		}
+		if ( empty($string) )
+			return;
+		if ( $this->in_loop )
+			echo "$string<br />\n";
+		else
+			echo "<p>$string</p>\n";
+	}
+
+	/**
+	 */
+	public function header() {
+		// Nothing, This will be displayed within a iframe.
+	}
+
+	/**
+	 */
+	public function footer() {
+		// Nothing, This will be displayed within a iframe.
+	}
+
+	/**
+	 *
+	 * @param string|WP_Error $error
+	 */
+	public function error($error) {
+		if ( is_string($error) && isset( $this->upgrader->strings[$error] ) )
+			$this->error = $this->upgrader->strings[$error];
+
+		if ( is_wp_error($error) ) {
+			$messages = array();
+			foreach ( $error->get_error_messages() as $emessage ) {
+				if ( $error->get_error_data() && is_string( $error->get_error_data() ) )
+					$messages[] = $emessage . ' ' . esc_html( strip_tags( $error->get_error_data() ) );
+				else
+					$messages[] = $emessage;
+			}
+			$this->error = implode(', ', $messages);
+		}
+		echo '<script type="text/javascript">jQuery(\'.waiting-' . esc_js($this->upgrader->update_current) . '\').hide();</script>';
+	}
+
+	/**
+	 */
+	public function bulk_header() {
+		$this->feedback('skin_upgrade_start');
+	}
+
+	/**
+	 */
+	public function bulk_footer() {
+		$this->feedback('skin_upgrade_end');
+	}
+
+	/**
+	 *
+	 * @param string $title
+	 */
+	public function before($title = '') {
+		$this->in_loop = true;
+		printf( '<h2>' . $this->upgrader->strings['skin_before_update_header'] . ' <span class="spinner waiting-' . $this->upgrader->update_current . '"></span></h2>', $title, $this->upgrader->update_current, $this->upgrader->update_count );
+		echo '<script type="text/javascript">jQuery(\'.waiting-' . esc_js($this->upgrader->update_current) . '\').css("display", "inline-block");</script>';
+		// This progress messages div gets moved via JavaScript when clicking on "Show details.".
+		echo '<div class="update-messages hide-if-js" id="progress-' . esc_attr($this->upgrader->update_current) . '"><p>';
+		$this->flush_output();
+	}
+
+	/**
+	 *
+	 * @param string $title
+	 */
+	public function after($title = '') {
+		echo '</p></div>';
+		if ( $this->error || ! $this->result ) {
+			if ( $this->error ) {
+				echo '<div class="error"><p>' . sprintf($this->upgrader->strings['skin_update_failed_error'], $title, '<strong>' . $this->error . '</strong>' ) . '</p></div>';
+			} else {
+				echo '<div class="error"><p>' . sprintf($this->upgrader->strings['skin_update_failed'], $title) . '</p></div>';
+			}
+
+			echo '<script type="text/javascript">jQuery(\'#progress-' . esc_js($this->upgrader->update_current) . '\').show();</script>';
+		}
+		if ( $this->result && ! is_wp_error( $this->result ) ) {
+			if ( ! $this->error ) {
+				echo '<div class="updated js-update-details" data-update-details="progress-' . esc_attr( $this->upgrader->update_current ) . '">' .
+					'<p>' . sprintf( $this->upgrader->strings['skin_update_successful'], $title ) .
+					' <button type="button" class="hide-if-no-js button-link js-update-details-toggle" aria-expanded="false">' . __( 'Show details.' ) . '</button>' .
+					'</p></div>';
+			}
+
+			echo '<script type="text/javascript">jQuery(\'.waiting-' . esc_js($this->upgrader->update_current) . '\').hide();</script>';
+		}
+
+		$this->reset();
+		$this->flush_output();
+	}
+
+	/**
+	 */
+	public function reset() {
+		$this->in_loop = false;
+		$this->error = false;
+	}
+
+	/**
+	 */
+	public function flush_output() {
+		wp_ob_end_flush_all();
+		flush();
+	}
+}