service worker: Refactoring around destroyed URL jobs.

This path is only for the non-S13nSW case because the URLRequestJob is a
weak ptr. Refactoring only.

Bug: 715640
Change-Id: I886b31f82173cb1bf9e22c950fc5bb0528c43b65
Reviewed-on: https://chromium-review.googlesource.com/1201509
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588319}
6 files changed