Index: wp-includes/theme.php
===================================================================
--- wp-includes/theme.php	(revision 34960)
+++ wp-includes/theme.php	(working copy)
@@ -233,6 +233,33 @@
 }
 
 /**
+ * Retrieve URI of current parent stylesheet.
+ *
+ * The stylesheet file name is 'style.css' which is appended to {@link
+ * get_template_directory_uri() template directory URI} path.
+ *
+ * @since 4.4.0
+ *
+ * @return string|bool URI to current parent stylesheet or false if no child theme is avtivated.
+ */
+function get_parent_stylesheet_uri() {
+	if ( ! is_child_theme() ) {
+		return false;
+	}
+	$template_dir_uri      = get_template_directory_uri();
+	$parent_stylesheet_uri = $template_dir_uri . '/style.css';
+	/**
+	 * Filter the URI of the current parent stylesheet.
+	 *
+	 * @since 4.4.0
+	 *
+	 * @param string $template_uri          Template URI for the current theme/parent theme.
+	 * @param string $parent_stylesheet_uri Template directory URI for the current theme/parent theme.
+	 */
+	return apply_filters( 'parent_stylesheet_uri', $parent_stylesheet_uri, $template_dir_uri );
+}
+
+/**
  * Retrieve localized stylesheet URI.
  *
  * The stylesheet directory for the localized stylesheet files are located, by