The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/03269741be10d52dc8e82c0ac524fdc5b9cf939d

commit 03269741be10d52dc8e82c0ac524fdc5b9cf939d
Author: Matt Falkenhagen <falken@chromium.org>
Date: Thu Sep 14 03:19:16 2017

service worker: Add UMA for the number of origins with a service worker.

This will help track adoption of service worker.

Bug:  764230 
Change-Id: Ia83d3ea81838a051161bb9788fbebffd6196a48b
Reviewed-on: https://chromium-review.googlesource.com/662857
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501856}
[modify] https://crrev.com/03269741be10d52dc8e82c0ac524fdc5b9cf939d/content/browser/service_worker/service_worker_metrics.cc
[modify] https://crrev.com/03269741be10d52dc8e82c0ac524fdc5b9cf939d/content/browser/service_worker/service_worker_metrics.h
[modify] https://crrev.com/03269741be10d52dc8e82c0ac524fdc5b9cf939d/content/browser/service_worker/service_worker_storage.cc
[modify] https://crrev.com/03269741be10d52dc8e82c0ac524fdc5b9cf939d/content/browser/service_worker/service_worker_storage_unittest.cc
[modify] https://crrev.com/03269741be10d52dc8e82c0ac524fdc5b9cf939d/tools/metrics/histograms/histograms.xml