title: Chrome's map to file system resource not working after update
body: <p>I can add a folder to the workspace (which doesn't seem to do anything, as far as I can tell), but the "map to file system resource" option seems to have been removed, and I can no longer live-edit css files.</p>
  
  <p>Is this a bug, or has the process for mapping css files been changed?</p>
  
  <p>This talk (<a href="https://developers.google.com/web/updates/2017/10/devtools-release-notes" rel="noreferrer">https://developers.google.com/web/updates/2017/10/devtools-release-notes</a>) says that the new version uses "magic" to map remote files to local ones, but I can't seem to get it to work at all.</p>
  
  <p>For reference, I'm trying to map a reddit css file to one on my own computer. It worked fine on a previous version of Chrome (basically I add the folder, and map the css file inside it, which has been renamed to have the same name as the remote one) but not on the new one (Chrome 63)</p>