The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/361cca9bb19c8af31feb06fd39fbbe21c60b99d1

commit 361cca9bb19c8af31feb06fd39fbbe21c60b99d1
Author: Mugdha Lakhani <nator@chromium.org>
Date: Wed Sep 05 09:45:37 2018

[Background Fetch] Add UKM metrics.

This adds the following metrics:

BackgroundFetch.HasTitle
BackgroundFetch.NumIcons
BackgroundFetch.DownloadTotal
BackgroundFetch.NumRequestsInFetch
BackgroundFetch.DeniedDueToPermissions

Bug:  877512 
Change-Id: I939ae4fc8e7e4abc1b322be8a9e09f00b168419a
Reviewed-on: https://chromium-review.googlesource.com/1193896
Reviewed-by: Peter Beverloo <peter@chromium.org>
Reviewed-by: Robert Kaplow (slow) <rkaplow@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Mugdha Lakhani <nator@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588807}
[modify] https://crrev.com/361cca9bb19c8af31feb06fd39fbbe21c60b99d1/chrome/browser/background_fetch/background_fetch_browsertest.cc
[modify] https://crrev.com/361cca9bb19c8af31feb06fd39fbbe21c60b99d1/content/browser/background_fetch/background_fetch_context.cc
[modify] https://crrev.com/361cca9bb19c8af31feb06fd39fbbe21c60b99d1/content/browser/background_fetch/background_fetch_context.h
[modify] https://crrev.com/361cca9bb19c8af31feb06fd39fbbe21c60b99d1/content/browser/background_fetch/background_fetch_metrics.cc
[modify] https://crrev.com/361cca9bb19c8af31feb06fd39fbbe21c60b99d1/content/browser/background_fetch/background_fetch_metrics.h
[modify] https://crrev.com/361cca9bb19c8af31feb06fd39fbbe21c60b99d1/tools/metrics/ukm/ukm.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668

commit 7431ee0cbf641a735c6e6cd91aafdc19f4cfd668
Author: Mugdha Lakhani <nator@chromium.org>
Date: Fri Sep 07 12:15:26 2018

[Background Fetch] Part 2: Add UKM metrics.

This adds the following metric:

BackgroundFetch.RatioOfIdealToChosenIconSize

Bug:  877512 
Change-Id: Id4289b13178ca9e3bd76e1ea9371f778788b5699
Reviewed-on: https://chromium-review.googlesource.com/1199591
Commit-Queue: Mugdha Lakhani <nator@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589496}
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/chrome/browser/background_fetch/background_fetch_browsertest.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/content/browser/background_fetch/background_fetch_context.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/content/browser/background_fetch/background_fetch_context.h
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/content/browser/background_fetch/background_fetch_metrics.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/content/browser/background_fetch/background_fetch_metrics.h
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/content/browser/background_fetch/background_fetch_service_impl.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/content/browser/background_fetch/background_fetch_service_impl.h
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/content/browser/background_fetch/background_fetch_service_unittest.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/public/platform/modules/background_fetch/background_fetch.mojom
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_bridge.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_bridge.h
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_icon_loader.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_icon_loader.h
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_icon_loader_test.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_manager.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_manager.h
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_update_ui_event.cc
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/third_party/blink/renderer/modules/background_fetch/background_fetch_update_ui_event.h
[modify] https://crrev.com/7431ee0cbf641a735c6e6cd91aafdc19f4cfd668/tools/metrics/ukm/ukm.xml

The part that's necessary before we ship is done. One more task remains here, tracked by  crbug.com/888454 . Closing this bug.