DevTools: Remove assertion when removing security origin.

Not that frames could be attached and navigated separatelyit is possible that we navigate/detach a frame
that does not have any security origin (it was attached but never navigated).

Drive-by: Add console.assert hook to inspector-test.js to catch incorrect assertions such problems in future.
Drive-by: Fix annother test that now fails due to incorrect assertion: baseURL is not mandatory on document.
E.g. baseURL might be null when document was created programmatically.

R=pfeldman_ooo, apavlov, eustas

Review URL: https://codereview.chromium.org/100223005

git-svn-id: svn://svn.chromium.org/blink/trunk@163881 bbb929c8-8fbe-4397-9dbb-9b2b20218538