Customizer: Use the `sandbox` attribute to prevent top navigation from the preview.

Props valchovski.
Fixes #42341.


Built from https://develop.svn.wordpress.org/trunk@44583


git-svn-id: http://core.svn.wordpress.org/trunk@44414 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/js/customize-controls.js

@@ -6289,6 +6289,7 @@
 				name: 'customize-' + previewFrame.channel()
 			} );
 			previewFrame.iframe.attr( 'onmousewheel', '' ); // Workaround for Safari bug. See WP Trac #38149.
+			previewFrame.iframe.attr( 'sandbox', 'allow-forms allow-modals allow-orientation-lock allow-pointer-lock allow-popups allow-popups-to-escape-sandbox allow-presentation allow-same-origin allow-scripts' );
 
 			if ( ! hasPendingChangesetUpdate ) {
 				previewFrame.iframe.attr( 'src', urlParser.href );

wp-includes/js/customize-preview.js

@@ -379,11 +379,6 @@
 			queryParams.customize_messenger_channel = api.settings.channel;
 		}
 		element.search = $.param( queryParams );
-
-		// Prevent links from breaking out of preview iframe.
-		if ( api.settings.channel ) {
-			element.target = '_self';
-		}
 	};
 
 	/**

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-beta1-44582';
+$wp_version = '5.1-beta1-44583';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.