title: Duplicate Completion Item Provider
body: <p>I have an instance of monaco editor running inside an iFrame inside of an angular 1.5 application. Whenever I load the editor, I use <code>registerCompletionItemProvider</code> to register a custom completion item. </p>
  
  <p>However, when the editor is loaded for a second time, the completion item is registered again and I get duplicate completion items. This happens each successive time that I load the editor. I don't know when the user is going to navigate away from the editor, and my controller does not have access to the monaco editor's <code>dispose()</code> method. How can I ensure that I don't continue to re-register existing completions? </p>
  
  <p>Thanks!</p>