I can continue to work on this, after metric CL is uploaded.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5c41b0a0bfa7b37e466d0a433687c2e591231efb

commit 5c41b0a0bfa7b37e466d0a433687c2e591231efb
Author: Xing Liu <xingliu@chromium.org>
Date: Fri Jul 14 19:16:46 2017

Move AllDownloadItemNotifier from content/public to components/download.

Originally it's in //chrome, and was moved to //content/public.
According to some discussion, now we decide to move it to
//components/download/content/public.

Also make download service use AllDownloadItemNotifier.

Bug:  736242 
Change-Id: Id709ffaa73366d97d55fabd75d6ccb2e6d611859
Reviewed-on: https://chromium-review.googlesource.com/556259
Commit-Queue: Xing Liu <xingliu@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486834}
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/android/download/download_manager_service.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/android/download/download_manager_service.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/chromeos/BUILD.gn
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/chromeos/drive/download_handler.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/chromeos/drive/download_handler.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/download/download_history.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/download/download_status_updater.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/download/download_status_updater.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/download/download_status_updater_unittest.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/download/download_ui_controller.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/download/download_ui_controller_unittest.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/extensions/BUILD.gn
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/extensions/api/downloads/downloads_api.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/extensions/api/downloads/downloads_api_unittest.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/ui/BUILD.gn
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/ui/webui/md_downloads/downloads_list_tracker.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/chrome/browser/ui/webui/md_downloads/downloads_list_tracker.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/components_unittests.filter
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/BUILD.gn
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/internal/BUILD.gn
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/internal/download_driver_impl.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/internal/download_driver_impl.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/internal/download_driver_impl_unittest.cc
[add] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/public/BUILD.gn
[add] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/public/all_download_item_notifier.cc
[add] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/public/all_download_item_notifier.h
[rename] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/components/download/content/public/all_download_item_notifier_unittest.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/content/browser/BUILD.gn
[delete] https://crrev.com/03b800c37e9643a72abb82fb9dc1050648ce3aa1/content/browser/download/all_download_item_notifier.cc
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/content/public/browser/BUILD.gn
[delete] https://crrev.com/03b800c37e9643a72abb82fb9dc1050648ce3aa1/content/public/browser/all_download_item_notifier.h
[modify] https://crrev.com/5c41b0a0bfa7b37e466d0a433687c2e591231efb/content/test/BUILD.gn