Across chrome://history, chrome://bookmarks, and the CrOS File Manager, we have different selection UX models.

We should standardize these for a consistent user experience. I think the File Manager's selection model is mostly fine, except that it needs a way to select disjoint sets (i.e shift select a few files and then ctrl + click a different file, then ctrl + shift + click to add another group of files, starting from the last ctrl + clicked file).

I'm going to change History into my desired selection model and then once there's consensus, we can port it everywhere else.