diff -r 490d5cc509ed -r cf61fcea0001 wp/wp-includes/customize/class-wp-customize-upload-control.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/customize/class-wp-customize-upload-control.php	Mon Oct 14 17:39:30 2019 +0200
@@ -0,0 +1,44 @@
+<?php
+/**
+ * Customize API: WP_Customize_Upload_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Upload Control Class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Media_Control
+ */
+class WP_Customize_Upload_Control extends WP_Customize_Media_Control {
+	public $type          = 'upload';
+	public $mime_type     = '';
+	public $button_labels = array();
+	public $removed = ''; // unused
+	public $context; // unused
+	public $extensions = array(); // unused
+
+	/**
+	 * Refresh the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 3.4.0
+	 *
+	 * @uses WP_Customize_Media_Control::to_json()
+	 */
+	public function to_json() {
+		parent::to_json();
+
+		$value = $this->value();
+		if ( $value ) {
+			// Get the attachment model for the existing file.
+			$attachment_id = attachment_url_to_postid( $value );
+			if ( $attachment_id ) {
+				$this->json['attachment'] = wp_prepare_attachment_for_js( $attachment_id );
+			}
+		}
+	}
+}