missing a cache validator

The following resources are missing a cache validator. Resources that do not specify a cache validator cannot be refreshed efficiently. Specify a Last-Modified or ETag header to enable cache validation for the following resources:
http://fonts.googleapis.com/earlyaccess/droidarabickufi.css
http://www.google.com/s2/favicons?...

AddDefaultCharset UTF-8

<IfModule mod_headers.c>
    <FilesMatch "\.(bmp|css|flv|gif|ico|jpg|jpeg|js|pdf|png|svg|swf|tif|tiff)$">
        Header set Last-Modified "Mon, 31 Aug 2009 00:00:00 GMT"
    </FilesMatch>
</IfModule>