title: dart error - could not start pub serve or connect to pub
body: <p>I'm trying to run <a href="https://www.dartlang.org/samples/dndfiles/" rel="nofollow">this</a> drag and drop API. When I try to run the dart file (with the dart editor) I get the following error:</p>
  
  <p><code>could not start pub serve or connect to pub</code>.</p>
  
  <p>I'm not very familiar with dart. Where's my error?</p>