Add missing string translation in widgets.

see #27453, #27112.

Built from https://develop.svn.wordpress.org/trunk@28140


git-svn-id: http://core.svn.wordpress.org/trunk@27971 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-customize-widgets.php

@@ -1041,7 +1041,7 @@ final class WP_Customize_Widgets {
 			'registeredSidebars' => array_values( $GLOBALS['wp_registered_sidebars'] ),
 			'registeredWidgets'  => $GLOBALS['wp_registered_widgets'],
 			'l10n'               => array(
-				'widgetTooltip' => ( 'Shift-click to edit this widget.' ),
+				'widgetTooltip' => __( 'Shift-click to edit this widget.' ),
 			),
 		);
 		foreach ( $settings['registeredWidgets'] as &$registered_widget ) {