Index: src/wp-includes/theme.php
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- src/wp-includes/theme.php	(revision c3615b26889514a0501ee6383f2622d944413dbf)
+++ src/wp-includes/theme.php	(date 1520005418000)
@@ -1904,8 +1904,9 @@
  *
  * @param array|string $stylesheet Optional. Stylesheet name or array thereof, relative to theme root.
  *                                 Defaults to 'editor-style.css'
+ * @param string       $version    Optional. Add version number to stylesheet URL for cache busting.
  */
-function add_editor_style( $stylesheet = 'editor-style.css' ) {
+function add_editor_style( $stylesheet = 'editor-style.css', $version = '' ) {
 	add_theme_support( 'editor-style' );
 
 	if ( ! is_admin() ) {
@@ -1913,14 +1914,21 @@
 	}
 
 	global $editor_styles;
+	global $wp_version;
+
 	$editor_styles = (array) $editor_styles;
 	$stylesheet    = (array) $stylesheet;
+	$version       = (array) $version;
+
 	if ( is_rtl() ) {
 		$rtl_stylesheet = str_replace( '.css', '-rtl.css', $stylesheet[0] );
 		$stylesheet[]   = $rtl_stylesheet;
 	}
 
-	$editor_styles = array_merge( $editor_styles, $stylesheet );
+	if ( '' == $version )
+		$version[0] = $wp_version;
+
+	$editor_styles = array_merge( $editor_styles, $stylesheet, $version );
 }
 
 /**