Fix some content/background overflow issues with commit graph lists

Summary: Ref T13552. There are currently some content overflow issues on the graph view where the menu height can exceed the content height and the frame is drawn on a sub-element. Make the frame draw around all the content.

Test Plan: Viewed commit graph history view, saw more sensible UI.

Maniphest Tasks: T13552

Differential Revision: https://secure.phabricator.com/D21440