Issue #2828888 by Jeremy: Add _drupal_file_scan_cache to memcache_stampede_protection_ignore

README.txt

@@ -148,6 +148,7 @@ example:
       'lookup_cache',
       'schema:runtime:*',
       'theme_registry:runtime:*',
+      '_drupal_file_scan_cache',
     ),
     // Ignore all cids in the 'cache' bin starting with 'i18n:string:'
     'cache' => array(

memcache.inc

@@ -522,6 +522,8 @@ class MemCacheDrupal implements DrupalCacheInterface {
         // the cache entry with a class destructor.
         'schema:runtime:*',
         'theme_registry:runtime:*',
+        // Not written until the end of drupal_page_footer()
+        '_drupal_file_scan_cache',
       ),
       // Disable stampede protection for cid prefix in 'cache'.
       'cache' => array(