Add ‘files-changed’ hook or add changed files to stats

I’d like to get a list of the changed files while in watch mode. The intent is to write a ‘test-runner’ plugin, so that once a test or react component is saved, the corresponding test would be run right away. I was taking a look at the source, and I think the only place this is surfaced is filesModified on https://github.com/webpack/webpack/blob/master/lib/Compiler.js#L101. I was thinking that it would be nice to add a new files-changed hook or dump the file change info into the stats, but is there a different way that the changed files list is surfaced?