DevTools: [Console] fix console in shared/service workers

The cachedResourceLoaded event not gonna happen in case of worker
frontend, so we should fetch console messages right away.

BUG=410313
R=vsevik

Review URL: https://codereview.chromium.org/544633003

git-svn-id: svn://svn.chromium.org/blink/trunk@181378 bbb929c8-8fbe-4397-9dbb-9b2b20218538