[ServiceWorker] Add wasFetchedViaServiceWorker flag to WebURLResponse and ResourceResponse.

If the request was fetched via a ServiceWorker, the URL of the response could be different from the URL of the original request.
So, we need to check the flag and the response URL in the ResourceFetcher::didReceiveResponse() and DocumentThreadableLoader::handleResponse() for CSP and CORS.

This wasFetchedViaServiceWorker flag will be set in chromium side code. http://crrev.com/375513002

The check code itself will be added in another change.

BUG=373120

Review URL: https://codereview.chromium.org/378473002

git-svn-id: svn://svn.chromium.org/blink/trunk@177661 bbb929c8-8fbe-4397-9dbb-9b2b20218538