Let me own this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/46b350aebb7adb9a0631f68f3c1ccf4d838d4adb

commit 46b350aebb7adb9a0631f68f3c1ccf4d838d4adb
Author: Kenichi Ishibashi <bashi@chromium.org>
Date: Thu Jun 21 03:19:22 2018

S13nSW: Record WriteResponseResult UMA

Record the UMA in ServiceWorkerNewScriptLoader as it uses
ServiceWorkerCacheWriter when S13nServiceWorker is enabled.

Bug:  852667 
Change-Id: I82007bcb8d6b1daee118d39e96570b1ba6921353
Reviewed-on: https://chromium-review.googlesource.com/1103432
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569143}
[modify] https://crrev.com/46b350aebb7adb9a0631f68f3c1ccf4d838d4adb/content/browser/service_worker/service_worker_new_script_loader.cc
[modify] https://crrev.com/46b350aebb7adb9a0631f68f3c1ccf4d838d4adb/content/browser/service_worker/service_worker_new_script_loader_unittest.cc
[modify] https://crrev.com/46b350aebb7adb9a0631f68f3c1ccf4d838d4adb/tools/metrics/histograms/histograms.xml