Don't use `array_merge()` when building comment children arrays.

`array_merge()` is much slower than building the combined array using a
`foreach` loop. The performance difference was causing a speed regression with
the `get_children()` functionality introduced in 4.4.

Merges [35931] to the 4.4 branch.

Props rogerhub.
Fixes #35025.

Built from https://develop.svn.wordpress.org/branches/4.4@35932


git-svn-id: http://core.svn.wordpress.org/branches/4.4@35896 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/comment-template.php

@@ -1330,11 +1330,16 @@ function comments_template( $file = '/comments.php', $separate_comments = false
 	// Trees must be flattened before they're passed to the walker.
 	$comments_flat = array();
 	foreach ( $_comments as $_comment ) {
-		$comments_flat = array_merge( $comments_flat, array( $_comment ), $_comment->get_children( array(
+		$comments_flat[]  = $_comment;
+		$comment_children = $_comment->get_children( array(
 			'format' => 'flat',
 			'status' => $comment_args['status'],
 			'orderby' => $comment_args['orderby']
-		) ) );
+		) );
+
+		foreach ( $comment_children as $comment_child ) {
+			$comments_flat[] = $comment_child;
+		}
 	}
 
 	/**

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4.1-alpha-35921';
+$wp_version = '4.4.1-alpha-35932';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.