diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-admin/includes/class-wp-upgrader-skin.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-admin/includes/class-wp-upgrader-skin.php	Mon Oct 14 17:39:30 2019 +0200
@@ -0,0 +1,203 @@
+<?php
+/**
+ * Upgrader API: WP_Upgrader_Skin class
+ *
+ * @package WordPress
+ * @subpackage Upgrader
+ * @since 4.6.0
+ */
+
+/**
+ * Generic Skin for the WordPress Upgrader classes. This skin is designed to be extended for specific purposes.
+ *
+ * @since 2.8.0
+ * @since 4.6.0 Moved to its own file from wp-admin/includes/class-wp-upgrader-skins.php.
+ */
+class WP_Upgrader_Skin {
+
+	public $upgrader;
+	public $done_header = false;
+	public $done_footer = false;
+
+	/**
+	 * Holds the result of an upgrade.
+	 *
+	 * @since 2.8.0
+	 * @var string|bool|WP_Error
+	 */
+	public $result = false;
+	public $options = array();
+
+	/**
+	 *
+	 * @param array $args
+	 */
+	public function __construct($args = array()) {
+		$defaults = array( 'url' => '', 'nonce' => '', 'title' => '', 'context' => false );
+		$this->options = wp_parse_args($args, $defaults);
+	}
+
+	/**
+	 *
+	 * @param WP_Upgrader $upgrader
+	 */
+	public function set_upgrader(&$upgrader) {
+		if ( is_object($upgrader) )
+			$this->upgrader =& $upgrader;
+		$this->add_strings();
+	}
+
+	/**
+	 */
+	public function add_strings() {
+	}
+
+	/**
+	 * Sets the result of an upgrade.
+	 *
+	 * @since 2.8.0
+	 *
+	 * @param string|bool|WP_Error $result The result of an upgrade.
+	 */
+	public function set_result( $result ) {
+		$this->result = $result;
+	}
+
+	/**
+	 * Displays a form to the user to request for their FTP/SSH details in order
+	 * to connect to the filesystem.
+	 *
+	 * @since 2.8.0
+	 * @since 4.6.0 The `$context` parameter default changed from `false` to an empty string.
+	 *
+	 * @see request_filesystem_credentials()
+	 *
+	 * @param bool   $error                        Optional. Whether the current request has failed to connect.
+	 *                                             Default false.
+	 * @param string $context                      Optional. Full path to the directory that is tested
+	 *                                             for being writable. Default empty.
+	 * @param bool   $allow_relaxed_file_ownership Optional. Whether to allow Group/World writable. Default false.
+	 * @return bool False on failure, true on success.
+	 */
+	public function request_filesystem_credentials( $error = false, $context = '', $allow_relaxed_file_ownership = false ) {
+		$url = $this->options['url'];
+		if ( ! $context ) {
+			$context = $this->options['context'];
+		}
+		if ( !empty($this->options['nonce']) ) {
+			$url = wp_nonce_url($url, $this->options['nonce']);
+		}
+
+		$extra_fields = array();
+
+		return request_filesystem_credentials( $url, '', $error, $context, $extra_fields, $allow_relaxed_file_ownership );
+	}
+
+	/**
+	 */
+	public function header() {
+		if ( $this->done_header ) {
+			return;
+		}
+		$this->done_header = true;
+		echo '<div class="wrap">';
+		echo '<h1>' . $this->options['title'] . '</h1>';
+	}
+
+	/**
+	 */
+	public function footer() {
+		if ( $this->done_footer ) {
+			return;
+		}
+		$this->done_footer = true;
+		echo '</div>';
+	}
+
+	/**
+	 *
+	 * @param string|WP_Error $errors
+	 */
+	public function error($errors) {
+		if ( ! $this->done_header )
+			$this->header();
+		if ( is_string($errors) ) {
+			$this->feedback($errors);
+		} elseif ( is_wp_error($errors) && $errors->get_error_code() ) {
+			foreach ( $errors->get_error_messages() as $message ) {
+				if ( $errors->get_error_data() && is_string( $errors->get_error_data() ) )
+					$this->feedback($message . ' ' . esc_html( strip_tags( $errors->get_error_data() ) ) );
+				else
+					$this->feedback($message);
+			}
+		}
+	}
+
+	/**
+	 *
+	 * @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;
+		show_message($string);
+	}
+
+	/**
+	 */
+	public function before() {}
+
+	/**
+	 */
+	public function after() {}
+
+	/**
+	 * Output JavaScript that calls function to decrement the update counts.
+	 *
+	 * @since 3.9.0
+	 *
+	 * @param string $type Type of update count to decrement. Likely values include 'plugin',
+	 *                     'theme', 'translation', etc.
+	 */
+	protected function decrement_update_count( $type ) {
+		if ( ! $this->result || is_wp_error( $this->result ) || 'up_to_date' === $this->result ) {
+			return;
+		}
+
+		if ( defined( 'IFRAME_REQUEST' ) ) {
+			echo '<script type="text/javascript">
+					if ( window.postMessage && JSON ) {
+						window.parent.postMessage( JSON.stringify( { action: "decrementUpdateCount", upgradeType: "' . $type . '" } ), window.location.protocol + "//" + window.location.hostname );
+					}
+				</script>';
+		} else {
+			echo '<script type="text/javascript">
+					(function( wp ) {
+						if ( wp && wp.updates.decrementCount ) {
+							wp.updates.decrementCount( "' . $type . '" );
+						}
+					})( window.wp );
+				</script>';
+		}
+	}
+
+	/**
+	 */
+	public function bulk_header() {}
+
+	/**
+	 */
+	public function bulk_footer() {}
+}