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