Accessibility: Add a default title for the media modal dialog.

Makes sure the media modal dialog `h1` heading isn't empty when custom media frames don't set a title. This is particularly important now that the media modal is an ARIA dialog, as the title is referenced by an `aria-labelledby` attribute to properly label the dialog.

Props donmhico, audrasjb.
Fixes #47612.

Built from https://develop.svn.wordpress.org/trunk@45925


git-svn-id: http://core.svn.wordpress.org/trunk@45736 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/js/media-views.js

@@ -2903,6 +2903,7 @@ module.exports = Frame;
 /***/ (function(module, exports) {
 
 var Frame = wp.media.view.Frame,
+	l10n = wp.media.view.l10n,
 	$ = jQuery,
 	MediaFrame;
 
@@ -2936,7 +2937,7 @@ MediaFrame = Frame.extend(/** @lends wp.media.view.MediaFrame.prototype */{
 		Frame.prototype.initialize.apply( this, arguments );
 
 		_.defaults( this.options, {
-			title:    '',
+			title:    l10n.mediaFrameDefaultTitle,
 			modal:    true,
 			uploader: true
 		});

wp-includes/media.php

@@ -3764,6 +3764,7 @@ function wp_enqueue_media( $args = array() ) {
 
 	$strings = array(
 		// Generic
+		'mediaFrameDefaultTitle'      => __( 'Media' ),
 		'url'                         => __( 'URL' ),
 		'addMedia'                    => __( 'Add Media' ),
 		'search'                      => __( 'Search' ),

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45924';
+$wp_version = '5.3-alpha-45925';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.