Merge branch '4.4' into 5.1

* 4.4:
  Enable "native_constant_invocation" CS rule
  Make AbstractPhpFileCacheWarmer public

UrlPackage.php

@@ -123,7 +123,7 @@ private function getSslUrls(array $urls)
         foreach ($urls as $url) {
             if ('https://' === substr($url, 0, 8) || '//' === substr($url, 0, 2)) {
                 $sslUrls[] = $url;
-            } elseif (null === parse_url($url, PHP_URL_SCHEME)) {
+            } elseif (null === parse_url($url, \PHP_URL_SCHEME)) {
                 throw new InvalidArgumentException(sprintf('"%s" is not a valid URL.', $url));
             }
         }