DevTools: fix "Disable Javascript" checkbox glitch.

Settings checkbox UI state was changed from outside, that confused control.

BUG=402406

Review URL: https://codereview.chromium.org/640633007

git-svn-id: svn://svn.chromium.org/blink/trunk@183880 bbb929c8-8fbe-4397-9dbb-9b2b20218538