DevTools: Move worker and device-inspection detection methods off the WebInspector ns.

R=eustas, pfeldman, vsevik

Review URL: https://codereview.chromium.org/196343013

git-svn-id: svn://svn.chromium.org/blink/trunk@169245 bbb929c8-8fbe-4397-9dbb-9b2b20218538