Allow users to override default gallery settings in JS via `wp_localize_script()`. This is already possible in PHP by filtering `shortcode_atts_gallery`.

Fixes #28693.

Built from https://develop.svn.wordpress.org/trunk@28990


git-svn-id: http://core.svn.wordpress.org/trunk@28778 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/media-editor.js

@@ -577,11 +577,7 @@
 		});
 	};
 
-	wp.media.gallery = new wp.media.collection({
-		tag: 'gallery',
-		type : 'image',
-		editTitle : wp.media.view.l10n.editGalleryTitle,
-		defaults : {
+	wp.media.galleryDefaults = {
 		itemtag: 'dl',
 		icontag: 'dt',
 		captiontag: 'dd',
@@ -591,7 +587,17 @@
 		order: 'ASC',
 		id: wp.media.view.settings.post && wp.media.view.settings.post.id,
 		orderby : 'menu_order ID'
+	};
+
+	if ( wp.media.view.settings.galleryDefaults ) {
+		_.extend( wp.media.galleryDefaults, wp.media.view.settings.galleryDefaults );
 	}
+
+	wp.media.gallery = new wp.media.collection({
+		tag: 'gallery',
+		type : 'image',
+		editTitle : wp.media.view.l10n.editGalleryTitle,
+		defaults : wp.media.galleryDefaults
 	});
 
 	/**