service worker: Remove dead code around ServiceWorkerResponseInfo.

This CL removes some dead code following the launch of
S13nServiceWorker:
* OnPrepareToRestart() for navigations which has no callsites.
* ServiceWorkerResponseInfo which was only possibly created in
  ForRequest(), but all callsites now pass |create| = false.

This removes code from ClearSiteDataThrottle which has not been
needed since S13nServiceWorker. The requests directly handled
and responded to by the SW no longer reach
ClearSiteDataThrottle::HandleHeader() at all. Furthermore, when
the network service is enabled, this file will be deleted as
ClearSideDataHandler handles the Clear-Site-Data directive.
The test for this is ClearSiteDataHandlerBrowserTest.ServiceWorker
which still passes before and after this CL.

Bug: 926114
Change-Id: Ib2a221a3711bdaaa89b7ddd3771ac8bf3bbca314
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1567149
Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#651196}
12 files changed