Thanks for checking!
In general, if there aren't specific owners for files or a directory, you can just pick an owner from a parent directory, so anyone relevant from content/browser/OWNERS or even content/OWNERS is sufficient. For a CL like yours in a specific area like drag and drop, it's useful to get a knowledgeable reviewer to approve first (e.g., the Microsoft reviewer you mention, or other such reviewers within Google) even if they're not an owner, and then a more general owner can take a look.
More specific to your note about Aura owners, that raises the question of whether we should try to add more after the last one was removed in
http://crrev.com/c/3705678. (Thanks for the link to that CL on chat.) I'm open to thoughts on that from the other content owners-- I personally don't have much Aura knowledge and would be happy to have Aura changes in content/browser/web_contents approved by someone more familiar.
Thoughts?
Charlie