DevTools: Show blackbox infobar on documents also.

Documents can contain scripts, so turn on blackboxing in this case also.

R=vsevik, pfeldman

Review URL: https://codereview.chromium.org/599433002

git-svn-id: svn://svn.chromium.org/blink/trunk@182489 bbb929c8-8fbe-4397-9dbb-9b2b20218538