Remove unnecessary methods and collapse function calls in the preloader code

- Remove PreloadRequest::defer()
- Remove ResourceFetcher::requestPreload(). The only user is preload()
  and is just calling requestPreload().
- Move setDefer() call in HTMLResourcePreloader::preload() into
  resourceRequest() call
- Make HTMLResourcePreloader::preload() private

R=japhet
BUG=none

Review URL: https://codereview.chromium.org/717453002

git-svn-id: svn://svn.chromium.org/blink/trunk@185100 bbb929c8-8fbe-4397-9dbb-9b2b20218538
ServiceWorker: Remove outdated InstallEvent::replace()

This function was removed from the spec:
https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#install-event-section

BUG=423600
TEST=n/a

Review URL: https://codereview.chromium.org/690393003

git-svn-id: svn://svn.chromium.org/blink/trunk@185101 bbb929c8-8fbe-4397-9dbb-9b2b20218538