Merged in feature/from-pantheon (pull request #16)

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo/src/conditionals/third-party/polylang-conditional.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Yoast\WP\SEO\Conditionals\Third_Party;
+
+use Yoast\WP\SEO\Conditionals\Conditional;
+
+/**
+ * Conditional that is only met when the Polylang plugin is active.
+ */
+class Polylang_Conditional implements Conditional {
+
+	/**
+	 * Checks whether the Polylang plugin is installed and active.
+	 *
+	 * @return bool Whether Polylang is installed and active.
+	 */
+	public function is_met() {
+		return \defined( 'POLYLANG_FILE' );
+	}
+}