Simply using dart formatter causes runaway processes

I'm sometimes seeing Emacs using quite a bit of CPU. Appears to be the dart analysis server, started by dart-server.el when looking for the dartfmt executable. I don't think I'm using the dart-server analysis server for anything else.

Start in dart-server.el, especially the path that looks for the dartfmt executable and starts the Dart analysis server. Reproduce formatter use while monitoring Emacs and child processes, then identify why processes continue running and verify that formatting no longer causes runaway analysis-server activity.

Written by the indexing model from the issue text.