require the XML PHP extension

composer.json

@@ -17,6 +17,7 @@
     ],
     "require": {
         "php": ">=5.3.9",
+        "ext-xml": "*",
         "doctrine/common": "~2.4",
         "paragonie/random_compat": "~1.0",
         "symfony/polyfill-apcu": "~1.1",

src/Symfony/Bundle/DebugBundle/composer.json

@@ -17,6 +17,7 @@
     ],
     "require": {
         "php": ">=5.3.9",
+        "ext-xml": "*",
         "symfony/http-kernel": "~2.6",
         "symfony/twig-bridge": "~2.6",
         "symfony/var-dumper": "~2.6"

src/Symfony/Bundle/SecurityBundle/composer.json

@@ -17,6 +17,7 @@
     ],
     "require": {
         "php": ">=5.3.9",
+        "ext-xml": "*",
         "symfony/security": "~2.7",
         "symfony/security-acl": "~2.7",
         "symfony/http-kernel": "~2.7"