[ServiceWorker] Treat opaque response as a network error for frame loading.

Currently we can read the body of the opaque response using iframe's innerHTML.
To prevent this we have to treat the opaque response as a network error for the frame loading.

This CL depends on https://codereview.chromium.org/625513002/ and https://codereview.chromium.org/623663002/.

BUG=411174
TEST=LayoutTests/http/tests/serviceworker/fetch-frame-resource.html

Review URL: https://codereview.chromium.org/621003002

git-svn-id: svn://svn.chromium.org/blink/trunk@183186 bbb929c8-8fbe-4397-9dbb-9b2b20218538