Contextual links within the Views UI preview are broken

Assign to myself.

So far this should work, though there is one fundamental issue behind it (which probably also causes contextual filters to fail).
The actual POST request produces a 302 which leads to a GET request, which does not have the ajax_page_state attached anymore,
which automatically leads to the problem that no new js is added.

    // It is highly suspicious if $_POST['ajax_page_state'][$type] is empty,
    // since the base page ought to have at least one JS file and one CSS file
    // loaded. It probably indicates an error, and rather than making the page
    // reload all of the files, instead we return no new files.
    if (empty($_POST['ajax_page_state'][$type])) {
      $items[$type] = array();
    }

For reference i uploaded both the network output of d7 and d8 when you click on preview.

This one has a dependency on #1841442: Contextual filters are broken in the Views UI preview, so this actual code can be already reviewed

#2: drupal-1837982-2.patch queued for re-testing.

#2: drupal-1837982-2.patch queued for re-testing.

The tests are looking great, so they are looking RTBC.

This means we seriously lacking tests ;). Good job in finding/fixing this and writing a test for it. Go VDC team!

#9: vdc-1837982-9.patch queued for re-testing.

Back to rtbc.

Committed/pushed to 8.x, thanks!