Reader mode URI handler doesn't steal data from current tab
When entering reader mode, there's a big delay to reload the page content from the network. This should happen instantly. I think the problem is that the reader mode scheme handler is based on the view source handler, which looks through all other open tabs to steal the page data. That works for view source mode because view source always opens in a new tab, not the original tab. For reader mode, the original tab displays reader mode, so we always wind up in the fallback case where the data has to be grabbed from the network again.