Bootstrap: do not go gentle into that good night r38411, r38412, and parts of r38389.

See #36335.


git-svn-id: https://develop.svn.wordpress.org/trunk@38470 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/customize/class-wp-customize-selective-refresh.php

@@ -67,6 +67,7 @@ final class WP_Customize_Selective_Refresh {
 	 */
 	public function __construct( WP_Customize_Manager $manager ) {
 		$this->manager = $manager;
+		require_once( ABSPATH . WPINC . '/customize/class-wp-customize-partial.php' );
 
 		add_action( 'customize_preview_init', array( $this, 'init_preview' ) );
 	}