Pin the admin menu on scrolling similarly to how the side metaboxes are pinned on the Edit Post screen, first run. See #29806.
Built from https://develop.svn.wordpress.org/trunk@29835


git-svn-id: http://core.svn.wordpress.org/trunk@29599 1a063a9b-81f0-0310-95a4-ce76da25c4cd