We realized that moving this histogram into renderer process isn't as easy as we expected. The histogram gave us some information but we haven't checked them frequently so we are going to remove this for now. We may re-add them as needed.

Current ratio on desktop is like:
desktop:
- None: 60-65%
- Some: 15%
- All: 20-25%
mobile:
- None: 20%
- Some: 40%
- All: 20%

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/127b0880355cbe09aad0750544db727fb61e2221

commit 127b0880355cbe09aad0750544db727fb61e2221
Author: Kenichi Ishibashi <bashi@chromium.org>
Date: Mon Jul 02 08:37:01 2018

Remove ServiceWorker.EventHandledRatioType.{Foreign,}Fetch

We found that these histograms are not very useful. We would
like to remove them because when S13nServiceWorker is enabled
these histograms are not recorded for subresource requests,
which may be a bit confusing.

Bug:  852670 
Change-Id: I6a6b036e239cc8d8b5e3475ab325937e9e05cc7f
Reviewed-on: https://chromium-review.googlesource.com/1117731
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571839}
[modify] https://crrev.com/127b0880355cbe09aad0750544db727fb61e2221/content/browser/service_worker/service_worker_metrics.cc
[modify] https://crrev.com/127b0880355cbe09aad0750544db727fb61e2221/content/browser/service_worker/service_worker_metrics.h
[modify] https://crrev.com/127b0880355cbe09aad0750544db727fb61e2221/content/browser/service_worker/service_worker_version.cc
[modify] https://crrev.com/127b0880355cbe09aad0750544db727fb61e2221/content/browser/service_worker/service_worker_version.h
[modify] https://crrev.com/127b0880355cbe09aad0750544db727fb61e2221/tools/metrics/histograms/histograms.xml

Closing as Fixed. We may re-open or file a new bug when we re-add them.