Blocked link to font source does not emit error event

[Patrick Griffis]

There are a couple of WPT tests that rely on the onerror handler being called when a font source is blocked by CSP.

They can be seen here: https://wpt.fyi/results/content-security-policy/font-src?label=master&label=experimental&product=safari&product=webkitgtk

But a snippet is:

      var link = document.createElement('link');
      link.rel="preload";
      link.as="font";
      link.href="http://{{hosts[alt][]}}:{{ports[http][0]}}/fonts/Ahem.ttf?font-none-blocked";
      link.onload = t.unreached_func("Should not have loaded the font.");
      link.onerror = t.step_func_done();
      document.getElementsByTagName('head')[0].appendChild(link);

[Radar WebKit Bug Importer]

<rdar://problem/88389961>

[Ryan Reno]

This was fixed by https://bugs.webkit.org/show_bug.cgi?id=246663