Script Loader: Fix protocol-relative URLs for the preconnect relation type.

`wp_resource_hints()` parses the URL for the `preconnect` and `dns-prefetch` relation types to ensure correct values for both. While protocol-relative URLs are supported for `dns-prefetch`, the double slash was lost for `preconnect`.

Props swissspidy, peterwilsoncc.
Props azaozz for review.
Fixes #37652.
Built from https://develop.svn.wordpress.org/trunk@38255


git-svn-id: http://core.svn.wordpress.org/trunk@38196 1a063a9b-81f0-0310-95a4-ce76da25c4cd

Author: ocean90

wp-includes/general-template.php

@@ -2839,12 +2839,11 @@ function wp_resource_hints() {
 					continue;
 				}
 
-				if ( 'dns-prefetch' === $relation_type ) {
-					$url = '//' . $parsed['host'];
-				} else if ( ! empty( $parsed['scheme'] ) ) {
+				if ( 'preconnect' === $relation_type && ! empty( $parsed['scheme'] ) ) {
 					$url = $parsed['scheme'] . '://' . $parsed['host'];
 				} else {
-					$url = $parsed['host'];
+					// Use protocol-relative URLs for dns-prefetch or if scheme is missing.
+					$url = '//' . $parsed['host'];
 				}
 			}
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38254';
+$wp_version = '4.7-alpha-38255';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.