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

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo/admin/metabox/class-metabox-null-tab.php

@@ -0,0 +1,30 @@
+<?php
+/**
+ * WPSEO plugin file.
+ *
+ * @package WPSEO\Admin
+ */
+
+/**
+ * Generates the HTML for a metabox tab.
+ */
+class WPSEO_Metabox_Null_Tab implements WPSEO_Metabox_Tab {
+
+	/**
+	 * Returns the html for the tab link.
+	 *
+	 * @return string|null
+	 */
+	public function link() {
+		return null;
+	}
+
+	/**
+	 * Returns the html for the tab content.
+	 *
+	 * @return string|null
+	 */
+	public function content() {
+		return null;
+	}
+}