DevTools: Fix order of CSS and JS resources in devtools.html

In order to ensure parallel loading of external CSS stylesheets,
they should be listed before the first JS resource.

R=eustas, pfeldman

Review URL: https://codereview.chromium.org/275563004

git-svn-id: svn://svn.chromium.org/blink/trunk@173857 bbb929c8-8fbe-4397-9dbb-9b2b20218538