Move DiffFileIndexView out into its own file.
Review Request #4642 — Created Sept. 24, 2013 and submitted — Latest diff uploaded
Move DiffFileIndexView out into its own file.
This isn't used anywhere except the DiffViewerPageView, but neither are any of
the other views that make up the diff viewer, and the page view implementation
is a pretty big file.
Smoke tested the diff viewer.