service worker: Add traces in ServiceWorkerFetchDispatcher

This is a follow-up CL of crrev.com/c/1511173. It removed netlog.
Add equivalent traces.

Bug: 939719
Change-Id: I9003c4348e19edca278e9b6ede49b2bbbee43e01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1513799
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#639426}
1 file changed