Earlier quoted context omitted.
I don't know why they went with patch files instead of forking chromium and rebasing the changes via git. They document how developers should "rebase" chromium: https://github.com/brave/brave-browser/wiki/Chromium-rebases... And it looks like way more work than doing it with git via git rebase chromium/master
If you do that kind of rebase you have to force-push to your branch, and that's not great for many reasons. The other option is to `git merge chromium/master` into your fork. This way you don't have to force-push, but the history is not that clean and bisecting can be tricky.
But with manually editing .patch files you need to manually find out how to resolve the conflicts, while in a rebase git at least shows you the merge conflicts.