Merge remote-tracking branch 'tango/MAGETWO-37783' into S53_bugs

Author: Dmytro Poperechnyy

app/code/Magento/Cms/Setup/InstallData.php

@@ -252,6 +252,10 @@ public function install(ModuleDataSetupInterface $setup, ModuleContextInterface
                 <th>EXTERNAL_NO_CACHE</th>
                 <td>A flag, which indicates whether caching is disabled or not.</td>
             </tr>
+            <tr>
+                <th>FORM_KEY</th>
+                <td>Stores form key used by page cache functionality.</td>
+            </tr>
             <tr>
                 <th>FRONTEND</th>
                 <td>You sesssion ID on the server.</td>