[ServiceWorker] Introduce skipServiceWorker flag to blink::WebURLRequest and blink::ResourceRequest

If the request is a force refresh (shift+refresh) the request should not be handled by the ServiceWorker.
https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#navigator-service-worker-controller

Currently we are checking LOAD_BYPASS_CACHE flag of net::URLRequest in ServiceWorkerControlleeRequestHandler::MaybeCreateJob().
But this flag is set not only when shift+refresh but also when devtool's "Disable cache" is checked.

To distinguish them, I want to add skipServiceWorker flag to blink::WebURLRequest and blink::ResourceRequest and SKIP_SERVICE_WORKER flag to net::URLRequest.

This is blink side patch.
Chromium side patch is this.
  https://codereview.chromium.org/527713002/

BUG=402093
TEST=none

Review URL: https://codereview.chromium.org/527703002

git-svn-id: svn://svn.chromium.org/blink/trunk@181155 bbb929c8-8fbe-4397-9dbb-9b2b20218538